It might work in campaigns (saveVar probably doesn't care if you're in the intro, mission or outro), but I believe this is not something that can easily be fixed for SP. I distinctly remember that MacGuba's famous "Un-Impossible Mission" had some kind of cheat that allowed him to count the number of living/dead units left for the outro (all I remember was that he had to add and remove magazines and maybe do something with magazine counting commands...or something) - but it's very probable that whatever bug he used to do it has since been fixed.
Unless someone else can tell me otherwise, in which case: that'd be great!
But AFAIK, this isn't possible (in a single mission).
What do you need it for? Everyone knows that saving vars between mission and outro isn't something that is usually done or seen, so if there's a burning wreck of your guy is holding the "wrong" weapon, no-one is probably going to react.
Wolfrug out.