...
If he could have seen all that, would Xar have wanted to turn back time, even though that is impossible?
Possibly.
But...
Looking into other people's lives when they are not right in front of you, is also impossible...
Probably.
I say "probably" because turning back time and looking into other people's lives when they are not right in front of you, are both things that require the kind of Magic that we call "imagination". Xar had not developed that kind of Magic yet, any more than he could move objects with the sheer power of his mind, or fly without the helpful addition of wings.