At some point in a handicap game, I am quite behind. I fancy a corner invasion, but from what I can see, his best variation leaves me a L+1-group and him to move. So my invasion is an overplay (from what I can read). But I'm quite confident he will not find that line, in any case there are many ways for him to go wrong. Now, you are supposed to win handicap games by making only good moves ... And there IS a chance the worst case scenario becomes true. What to do ?
Bill: Well, you could make the invasion as a way of looking for a place to resign. :-)
BTW, as far as life and death are concerned, even pros playing teaching games do not assume perfect play by their opponents/students, but go ahead and make invasions that can be killed, or leave half-dead groups behind.
Andre Engels: I see no reason not to play the invasion. I don't know what you mean by the rule that one is supposed to win handicap games by making good moves, but I don't think it would really hold here. In my opinion, there is nothing against an overplay of this kind every now and again. What you should try to avoid, is to make bad shape or bad style moves which could be copied by the weaker player.
As another issue, depending on your own strength there might be a possibility of playing the invasion even in an even game. It probably will not succeed, but if it does, you suddenly have chances to win the game again, and if it does not, you have a good moment to resign.
dnerra: It depends an bit on how clear-cut it is. If you are not even 100% sure that would die with optimal play (as you seem to suggest), then I think there is nothing wrong with invading.
Or maybe your opponent tried to secure a big corner with an ambitious keima (instead of a safe sagari), because he believes to have read out the corner. Then let him show you what he read out. If he read it right, he deserves to win and you have found a place to resign. If he didn't -- well, then he did a gamble and deserves to lose (in the best spirit of a teaching game).
Charles I would say the knack of handicap play with White is knowing how to improve your position. Invasions that are potentially mochikomi risk not doing that, but the opposite; so carrying them out in a sense admits other ways are absent.