IMHO... Results stands. 5 in - 20 out. No reason to cancel the race. No rule supporting this decision. As far as some boats finished, means that to finish in the assignment time was possible. What the 5 boats did wrong to have their scoring cancelled?
Same as per option 1 and 2

i had a race like this once before a cut off to gold and silver fleets when there was a disparity of skill. in light airs it was obvious a lot of boat sould be out of time. the race committee requested redress based on the si being an error or ommission and the International jury gave redress finish plus 30 for preliminary rounds plus 15 again when split to gold and silver.

The time has to be related to the race length. different for a 30 min race to a two hour one.

things can be changed but it would be unusual.

Have to agree with Luigi. 5 boats sailed and finished withing the rules and they should be scored. 
I had a race, when 15 boats out of 48 finished in time limit. After 8 boats finished in 4 minutes, the wind totally dissaper and than another 10 manged to finish in time limit, which was 20 min. Target time was 50 and the first boat finish the race in 55 min. 
We depend on weather conditions and this is part of the game.

I tend to agree with the majority here - keep the race, as distasteful and "unfair" it might be.  A possible solution would be to continue to record finishes after the finishing window is closed, then request redress on behalf of the TLE boats - the RC error being that 15 minutes was too short a window - the redress would be their actual finishing positions.

On the other hand, did 20 TLEs really affect the results significantly?  In a two-race series (with presumably no discarded race), you would have to do fairly well in both races to be in the top 3 positions. 

The only "real" opportunity to abandon would be before the first boat finished.  After that, the hurdle becomes much higher.

Perhaps I could expand this discussion a little - let us assume this is a race for handicap dinghies and there is a time limit. Many boats finish within the time limit or the extended time limit following the first finisher but a number of the slower boats fail to finish in time and as set out in the SIs are scored out of time. A calculation of the handicap adjusted time for one of these slow boats shows that it actually would have won the race on handicap if it's result had been scored, How should a PC handle a request for redress from that boat ?
 

Just to answer S.Davidson's questions :
a: Yes
b: No

To answer Bill Handley's question - in this situation if it was not possible for the slow boat to score at all when the first boat home finishes at or just before the race time limit them that would IMHO be an ommission of the Race Committee. However it should have been spotted by the race committee a lot earlier when they saw the handicaps.
I was once forced by the OA to add a boat to a handicap race for a fleet of boats which were normally covered by about ten minutes an hour top to bottom.  This extra boat was around 12 minutes an hour faster then the fastest of the remaining fleet.  I amended the time limit to cope with this.

SIs are the responsibility of the Race Committee.  It would appear that a number of responders are blaming the OA.  It is the responsibility of the Race Committee to ensure that a race will be run fairly in the prevailing conditions.  It is perhaps unfortunate that in this case, the Race Committee did not set a length of course in the prevailing conditions that corresponded with the time limit.
It is an interesting concept for a Race Committee to seek redress on behalf of some competitors against themselves.
In a Race, the concept is surely to allow competitors to compete fairly against each other, and thereby identify the best sailors in those conditions.
In this particular instance, the top five sailors in the conditions were identified.  No specific unfair hinderance was mentioned that prevented the other competitors from finishing within the time limit; the lack of wind hindered everyone equally.

As a follow-up to Bill's question -- a secondary time limit (i.e., a time limit for boats to finish after the first boat finishes) is a bad idea for handicap fleets, as it clearly prejudices the slower boats.  I was once on a race committee that had to score a boat TLE, only to discover later that she was winning the race on corrected time when we did that! 

In response to Tony's comment about the RC filing for redress on the basis of their own action, it's not all that uncommon.  In fact, I think it's an option RCs should exercise more often.  I sat on a protest committee earlier this year when redress for a boat was sought by the RC based on their failure to signal an individual recall correctly. They scored the boat OCS and then requested redress for her.  The issue was not whether the RC had acted improperly, but how to make a fair and equitable adjustment to the boat's score.  That can only be done by a protest committee, after a hearing.

I support Luigi's and Rob's comments. The reason to have a secondary time limit is to ensure that consequent races can be started in reasonable time after the previous one has finished, and is not always needed. In handicap fleets the secondary time limit, after the first boat has finished, should always be bound to calculated time of each boat, not the absolute sailed time.

Keep results.

To Bill's expansion of the question when it's a handicap race and the finish-after-first-finish TL isn't long enough to overcome the handicap with plenty of buffer, then that is a failing in the SI's and I would think maybe a basis for redress.  I was the RC Chair for a fleet of 60+ PHRF boats which raced each week.  We spent quite a bit of thought each year splitting the fleets into PHRF-classes and thinking about a fair TL.  This was a Wed-night fleet, so we knew 6km was about max and worked out a fair (and fairly long) TL.

To Matt's suggestion that they could "keep racing", I don't think that can be fair to all boats unless there was a way for the RC to communicate to all boats that they were going to open a redress for the fleet.  If the SI's required all boats to monitor a VHF channel, then I can see how that could be done.  Otherwise, if I heard a gun and I had a 15 min TL, I'd have someone on my boat keeping track of it and we'd stop racing after it was clear we were TLE.

I'm with Luigi & Bogan - there's no good reason to abandon.

The discussion about redress is also interesting as I don't believe that it's an improper action of a RC to set an inadequate time limit in the SI. The RC has complete discression and surely, if it is permitted to make a decision that turns out to be a poor one, it's bad luck for the sailors, but Its not grounds for redress.

Re Phil's comment - if the RC set an "inadequate" time limit - is that not an improper action as it is at least inadequtae?  Personally I prefer to use only the additional time limit i.e Boats finishing 20 mins (or whatever) after the first will be scored DNF (paraphrasing ) and not include an overall time limit - not for all events but for dinghies and keeboats on short courses.