as was stated before, there's already a bonus in perk points for landing succesfully. Maybe the multiplier could be increased, but I still don't think that'd change many people's attitude in the MA.
Hmm, what about this, you don't get any score points if you don't RTB safely. You still get perk points, you still have your stats, you just don't gain points (for higher rank). It's an incentive to stay alive, but it doesn't affect gameplay one bit if you go out and die 10 sorties in a row. You still get perkies for everything you killed, you still can take off anytime you want, in any plane you want, with any loadout you want (under current system rules, obviously). Only thing is that's seen as a penalty for dying.
Aside from that, I like the kill streak ideas. You get more points for each kill streak in a row (if you land it safely, obviously, as that's the point here.) You go out and you kill 3 planes. First plane gets you some points right off the bat. Second plane gets you some points right off the bat, plus a possible bonus if you land. Third gives you immediate points, and an even greater bonus. You land, you have the points from the three kills, plus the bonus points (the 3rd kill got you a bigger bonus percentage than the 2nd.) You take off on another sortie, and it's kill #1 for the sortie, but kill #4 in terms of bonus. This could be displayed in kill buffer as Victory 1 (4) by Nifty of 332nd Flying Mongrels.
anyways, outta time, I'm going home!