Am I wrong in providing this feedback to a candidate?

It's been one day? There is some possibility of extraordinary circumstances (of which you can't possibly be aware at this point) explaining the situation that could paint things in a very different light.

Would you send a similar email to any of your other coworkers being missing with no contact for one workday?

BTW you need to blackbox names in te future, those green squiggles look reversible.

It may have helped you vent your (completely understandable) frustration, but that's about all it accomplishes. From your brief description and comment here, it sounds to me like this candidate's goal was just getting an offer letter to use as leverage to get a better deal from the place he really wanted to work at.

That's an awful practice, but is also reasonably common. I think a better response would have been to not say anything to the candidate at all, but just put him on your "do not hire" list and move on with your business.