Honestly, I'm gonna do a -1 due to how many cons there are.
Cons:
We are human and as humans, we can easily abuse/break anything new.
People like to change their minds at the last second. When it's too late, they lose everything and they have to start all over again.
Staff will have too many staff tickets/PK appeals to deal with due to this cyanide pill.
Like I have said before, we are human and we will abuse it. If a new player/injured player/hated player/rival comes across a veteran player with the cyanide pill, that veteran player will try to give that player the cyanide pill and convince that this is just ordinary pill to take. Or they'll just force them to take it!
Also, if player takes the pill and ends up breaking the rules. The staff will teleport them and decide their punishment only for that said player to die, causing staff to lengthen the ban due to LTAP.