I've seen estimates on the amount of US soldiers dead ranging from 0 to 180 while this article doesn't mention any deaths. It's crazy how large of a fluctuation there is, it's so hard to know what news sources are valid.
If casualties are non-zero, the President will be obliged to carry out his “52 targets” threat. This is probably the right move — don’t play tit-for-tat against a less powerful adversary, instead immediately escalate to a level they can’t possibly match.
Unfortunately Iran’s air defences are more potent than anyone the US has bombed recently, so we might be about to find out just how good US technology really is.
What happens next? I’m not sure. I can’t imagine the US committing to a ground invasion of Iran, but it should be possible with an air campaign to reduce Iran to the level of a 2000-era Iraq.
Edit: President Trump’s latest “all is well” tweet, and his intention to hold off on doing a briefing until tomorrow, seems to imply that US casualties were zero after all and that he’s chosen the “laugh it off” response, which is a great relief to me.