MORE: and most people did (voluntarily) "participate" (for the vast majority of people the option of suicide or effecting the end of one's life by other means was there fairly early on and, no, I do not think you would have had to be crazy or at least depressed to do that: it's a very basic choice... and there are rational reasons that cut both ways...) D.
probably nothing... "thanks for your participation!" and ... lights out! (although it looks like we might get a bit of a celebration at the end: things like a flash review of one's life and some sensory stimulation probably due to the brain getting less and less oxygen after vital functions have ceased and cells are still alive for a while...)
P.S. if this is what's going on and is inevitable, it makes no sense to be depressed about it! -- you still got to live and (hopefully) it was fun while it lasted... D.