Loki waved a hand. "I suspect that's down to you and yours, which is why I use if rather than when." For a wonder, he didn't doubt Thor. If there was a chance, Thor would take it if he saw it. But there was a chance he wouldn't see it because he wouldn't be looking, as well as strong argument and good reason for Thor's numerous Midgardian friends to ensure he stayed dead. Either way, Loki wouldn't have a say, so he didn't see the point in worrying over it.