I guess you haven’t suffered one of these yet then.
When this happened I had 3 hospitals, but no way was that enough beds to cope with that many patients.
And while I haven’t experienced it myself as I usually play Pacifist, hugh armies can turn up in the game demanding you pay them a sum in gold or they’ll attack your town with heavily armoured troops and battering rams.
And that double hit I had of smallpox and bubonic plague was on Pacifist setting on a Pioneer map btw so such events are not limited to playing non-Pacifist mode. Easiest setting in the game you can have.