I'm trying to remember whether I have ever found myself in this situation and if so, what I did. Luckily, since I decisively left Christianity I have not faced this decision, but I think it is clear in my mind how I would react.
It is not that I can be certain that there is no god - nobody can prove that. But I feel quite sure that the Christian God is so completely implausible that there would be no point in praying to him. Even if he did exist he doesn't have a great track record with me, even when I believed in him. Why would that change now that I don't?
So would I choose any other deity? I think not. Of all the gods that I have ever heard of, none of them seem any more plausible than God with a big G.
So I think that's my answer.
No, I wouldn't pray, whatever the situation.