Well, the obvious question is, have you checked the oil level? It's not a good idea to let an engine run when such messages appear, but te warning message could be an anomaly, arising from a sensor getting dire messages when the overheating occurred, but I wouldn't place too much of a bet on that. Did the message disappear while you left the engine running?
As a simple, practical matter, before any more elaborate diagnostics, I suggest changing the oil and filter as part of the repair routine here. After that, running the car for a bit and then visually examining the clean oil might give you some indication whether you have cylinder head damage.