I have heard of this mission, and a couple of others having this problem (I think "Caida Libre" and "The Long Stretch" are other missions that people have missed). Currently there is no workaround. If you've done all of the collectibles, remember that to get 100% completion, you only need to do half of the jumps, only half of the knife flights and under the bridge stunts, so you get a bit of a break if you've already done them all on your current file for the respective achievements. You still have to get all of the letter scraps and spaceship parts though.
My guess is Rockstar probably won't release a patch for this since they probably only care about making money off of GTA Online at this point, but even if they did patch it you probably would have to start a new game anyway. Sorry that this happened to you - I enjoyed the single player game but there's no way I would want to go back and do the collectibles and other random tasks again.