He was at least kind enough to "seal" demon king into an animal instead of letting him die. Or sealing him into a rock or gem.
a minor mercy... but then again - perhaps the demon king would have rather died with his "dignity".
It may be a major disrespect even beyond desecration of his corpse, to the demon king.
I know some degenerate's that would see it as the greatest reward.
I personally would prefer being sealed in a flof over death. I wouldn't be happy, but being alive is better than not being alive IMHO.
In the case of being alive as a flof, im not "crippled" or trapped, and in fact I have some freedom due to no longer having labor and rent/tax obligations and a body that is well suited to living completely exposed to the elements. Its better than being a prisoner or a stump, I guess.