Yes, you're right, female mantids have reputations to be mate eaters. However, in captivity (at least under my watch) I do everything possible to keep my males alive. This usually involves stuffing the female with multiple large meals before introducing the male, having the female chow on some food when introducing the male, and of course, human intervention if anything goes bad.
In the mating that occurred yesterday the male came out just fine... He'll live to mate again next week once he's "recharged".