Nail, by the rules the caster gets no special information when he's picked an invalid target. I agree that would be reasonable, but nothing in the RAW says it works that way.
Come to think of it, there are even more possible results than I had thought of:
- The spell is successful
- The victim makes his saving throw
- The victim's SR resists the spell
- The victim is immune due to mind blank or a similar effect
- The victim is in an antimagic field or some other non-scryable area
- The spell fizzles because the victim is not a valid target (and is possibly dead)
Only the first result will give the caster any information on what happened. He knows the spell worked because he can see the scried vision. For a targeted spell, rthe caster will also be aware when a successful save happens. But if a spell fails for any other reason, the caster doesn't necessarily know why. (Skip's article doesn't change this-- AFAICT it just repeats the rules already in the book.)
I think I need to retract my earlier suggestion.
Nightmare is only a useful tool here if the victim has no SR, and lacks access to protections like
antimagic field or
mind blank. Outside those limitations, it's hardly better than just casting
scrying again.
A better solution would be to use
commune or
contact other plane to ask whether the victim is still alive. Those will still fizzle if the victim is alive and has
mind blank running, but if that's the case you won't find any information about him no matter what you to.