The fuse in question is either a 15amp or a 20 amp ceramic fuse available at Lowes or Home depot. If changing the fuse fixes it, then you are good to go. However, it doesn't always fix it. There are 3 or more thermostats, door switches, a diode, a cap, a control board, a transformer, and a magnetron tube that could also be your problem. If you have a volt meter, these componets are easily checked. There are several good U tube videos that will show you how. Just be careful to discharge the cap before messing around in there as it can store enough juice to kill you.
If your problem turns out to be a thermostat, switch, diode, or cap, these are easily and cheaply replacable. Anything else, I would be looking for a new microwave. Since it died while you were cooking, my bet would be a thermostat.
Big Bob