In the past: Thank God you are fine! What if something had happened to you? Thank God you are fine! What if something happened to you? Thank God you are fine! What if something would have happened to you? something might be in future What if something happens to you? I will never forgive myself. What if something were to happen to you? I would never forgive myself. something might have happened and I'm asking it because of my curiosity What if something happened to you? What would I care? JK What if something happens to you? What if something had happened to you? What if something were to happen to you?

For me, 1. if something had happened... 3. if something would have happened...

"What if ..." is the short form of "What would you do if...?" 1. Past = Thank God you're safe. What if something HAD happened to you? (A lot of people forget to add "had" but it should be there if you want to use perfect grammar.) 2. OK 3. Hmmm... maybe not. I think you can simply ask, "Did something happen?" or (if you are sure that something happened) "What happened?" When you ask, "What if..." you assume that something DID NOT happen (or has not happened yet). If you think that maybe something happened, then you are no longer making this assumption. So you can't use "What if ..." I hope that helps!