Hopefully, your printer's firmware noticed what looks like a failed thermistor and emergency stopped on its own. If it didn't, I'd definitely test fail states for both the hotend and the bed thermistor, before putting this back into production. That level of overheating is concerning. :(
The problem was actually that when I switched nozzles, I smacked the heat compromised power source for heater core.
The firmware halted when the thermister registered no heat.
Remarkably, I somehow have a spare. I've ordered the correct terminators for the power, since my spare doesn't have those.
And I was on such a roll with printing lately