While I agree that the permanent spell will end if the corpse is destroyed that don't mean that death make a creature that has a permanent spell on it an invalid target for that spell.
When you check the target changes?
As I pointed out, if you check constantly any spell with a target of "creature touched2 will cease to work as soon as the caster isn't touching that creature anymore.
Other spells would fail as soon as they are cast if you check the target validity after the spell has been cast and the effect resolved.
If you are arguing that you need to check only on target death, please show us the specific rule saying that. It don't exist.
Yes, you would check continuously for target validity on all spells. Nothing to do with death as a "special" event. I agree it isn't.
I don't see any examples of spells that would be problems continuously evaluating targets. You offered some examples above, yes, but I don't see how they are problems either:
Does not have a target, so cannot possibly be an example of something with target issues.
The target is a creature, invisible creatures are still creatures, not a targeting problem.
"Touched" is PAST tense and so still holds true after you move your hand away.
Present tense would be "Creature you are touching" which is not what it says.
The only thing that would be remotely close to how you seem to be reading it would be [i]passive voice[/]i, which A) is poor writing and should never be ASSUMED by default, and B) still wouldn't be what it says anyway, it would be "being touched" if so.