[@Savato]
That could certainly kill him, although it again wouldn't work as a long-term failsafe because eventually he would become immune to it. By simply being in and around the effects of Green Lantern Rings he was able to develop a resistance to it. If you filled him with Reishi and immediately detonated it that would kill him, but if you left it there as a failsafe it would become steadily less effective until he was completely immune to it. Hence the problem with attaching a failsafe to Apocalypse/Doomsday. Given time, he'll adapt his way past any barrier, and escape any prison. This is why he's often described as the inevitable destruction of the Earth, a being that cannot be stopped and only delayed.