they'd just have a sniper kill her and warm up a clone. Unit 01 is the only thing that absolutely cannot be replaced. Also, Ranma would then be facing the entire might of the UN, who would want his scalp on the wall for threatening the entire world. And since the regular army can't fight Angels, an insanely powerful martial artist would be just the thing to vent their frustration on. Does he have a technique that will stop an N2 mine? A howitzer barrage? Poisoned food? 60 kilos of Mentos and a a barrel of Diet Coke?
If I were to write a fic of this nature. First they wouldn't know that Ranma was the one to kidnap her. Second they'd have no idea where Ranma is so that limits them a great deal. Ranma is one person in billions and he does know stealth techniques -enough that he probably could sneak into and out of NERV at will without them noticing, if Rei is cooperating with him his chances would go up a great deal. Basically I was thinking about how Ranma could screw with the Evangelion universe to the greatest degree without powering up Ranma artificially or setting Ranma as he possible might be when he is older (to what degree and how he gets more powerful is unknown but he does have lots of ways).
Ranma is not powerful enough to go against an angel as he is (given 10 years time after he's fully developed physical with more techniques, power, and understanding of how ki and magic works maybe who knows -his universe is full of power-up several of which he not only knows about but has access to) so I ruled that out immediately.
I don't really want Ranma to just some how become a pilot - done to often and don't want to go that route.
Basically very loose idea is Ranma sneaks into NERV sees how they are treating her and takes for the hills with her screwing their plans royally in the process.
Ranma can be poisoned happens even in the manga (temp paralysis tea, Kodachi's food, etc..) and he probably wouldn't survive a Nuke (or N2 mine which is basically a nuke). He's tough but not that tough (though I suppose if he had enough warning he might be able to get far enough away or do like Ryoga and tunnel deep enough into the earth so as to survive it). Ranma's good but an entire modern army is beyond his current abilities (an older army that doesn't have modern weaponry he could probably take depending on certain factors) and he probably depending on the tactics he uses could take down a good number of them before they manage to take him down (for instance they aren't likely to use heavy artillery if close in with there ranks). But they would also be limited majorily in not knowing his abilities, where he is, etc.. No matter how powerful there weapons or number of people they have it's not going to matter much if they don't know where to use them or is in a place where the cost in using them out weighs the advantage.
Also would the UN intervene they don't know of how important Rei is and Gendo maybe keeping quite in how important to his plans she is. So Ranma may for awhile at least only have to deal with NERV forces and commendered local police which would most likely be well within his ability to handle.