My crown fell off. What is the worst case scenario that is happening?

I would say that worst case scenario the tooth could have fractured and you would need to have the tooth removed and replaced by implant, bridge, etc.Other scenarios could be:1.  If the tooth has a root canal already, discoloration is common and they do not look the nicest when a crown is not covering over them.2.  The gum tissue could be inflamed from the crown being loose for a while prior to it coming completely out.You need to see a dentist asap to determine if there is any significant damage that has occurred.  Hopefully, and the best case scenario would be that the existing crown can be recemented back on.Either way, get in as soon as you can to see your dentist.  If you do not know a good dentist in your area let me know, I went to dental school in KC and know a few great dentists if you need a recommendation.

Worst case is if you do not go to the dentist right away to get the problem diagnosed, you will end up with a bigger problem to fix.  Usually crowns falling off with ugly stuff under them means the tooth fairy will be scheduling a visit with you.