I really admire your view-and-release policy. I try to encourage that when I can. However, my "campaign" is limited to native species, which the Praying Mantis is not, so as far as I'm concerned, the longer you keep it out of the wild, the better - although if it's already bred, the damage is done. Yes, I suspect you are prolonging this animal's life. I believe mantids usually die after breeding, and captivity is generally safer than the wild at any time of year.