When superman dies do the cells in his body still continue to absorb Earth's yellow rays and keep him invulnerable to damage or is it after he is he is slowly  depowered or is it after he dies it just ends and he decomposes like a normal body

Hmmmmmm. My guess is that the unimaginative people at DC decided to add a new power to Superman...IMMORTALITY..
I imagine the brain storming sessions at DC go something like this...
Hey what can we do different this time around...
Oh I know, lets give SUPES another power
Hmmm Doesn't he already have a power for everything?
uhhhh... wait..lets kill him..then not really..let him slowly regenerate...
Doesn't he already have a healing actor?
uh yeah but this will make him IMMORTAL...get it..he can't be killed... he will just keep absorbing energy until he comes back to life....

MAKES ME WONDER WHATS NEXT FOR THIS OVER POWERED BUFFOON

I think that when he was killed by Doomsday his body continued to absorb sunlight and this effectively jump started his body metabolism again.

yeah i see watt ur saying but thats just stupid as hell

In my opinion, you can't really overpower Superman.

As I understood it, Superman was still super strong even after death. They couldn't do c.p.r. or anything like that. So I don't think they did embalming process.