Thanks for the quick replies. I think I'm good. My bought a spare, but it's now in a different tank and I didn't replace it. This was a good fire drill . . .
I have had glass ones shatter (20 or so years ago) due to forgetting during a change and then dumping in fresh water. Obviously, it was super clear that the heater was toast at this point.
These are titanium, and I let them cool a bit before filling. There's a plastic cage around them that melted slightly on one, but they appear to be working okay.
please note that heaters can lose their efficiency after such accidents meaning it might still be heating but won't be able to raise the temp quickly enough. if you live somewhere temp swings are big its better to replace the heater.