Make a (large?) percentage of all Helos shot down repairable.
This would encourage: players to keep their expensive Apaches/Havocs safely behind their own lines, so if they were shot down, they at least have a second chance to get back into the action.
Also, it would be beneficial to keep them hidden behind decent cover, so they couldn't be sniped by ATGM's etc while being repaired on the ground
Helos killed over woods would be lost, again, discouraging that kind of recklessness from the player.
Imagine you have a Helo hot down behind enemy lines (on those occasions that warrant it), but undetected by the enemy. Sending out units on a rescue mission to guard/repair it would be nerve wracking fun no?
Please, try and shoot holes in the idea (or link to somewhere it's already been mentioned

). I can't see any obvious flaws, but I'm sure there are some.
Ps. AA would still be as efficient at shooting down Helos thus taking them out of the action for a period of time, and would gain experience in doing so, they just wouldn't accumulate so many points.