"gatt" writes:

But what if you fly someplace and, say, the alternator
fails while you're gone? You certainly don't fly back,

Why not? If the return flight is a couple of hours, get the battery
charged up, have someone handprop or use up some battery to crank it,
take off, turn off all the electricals and fly it home. If you need
to enter controlled airspace turn things back on briefly.