Secondly, I still don't get how the current on the one phase makes a return
path if the neutral is disconnected.

I know it's AC, but what's being described is like disconnecting one of the
leads to a battery. Maybe somebody can better describe the term 'broken
neutral wire'.

The 120V service in your house is between one of the hot legs of the
line from the pole and ground. If you look inside your breaker panel,
you'll see that the neutral from the pole, the white "neutrals" from all
the branch circuits, and the bare copper or green-jacketed "ground"
wires from the branches are all bonded together and to a grounding
electrode driven in your yard somewhere. So, assuming there is still
power at the hot legs of the service from the pole, there will still be
120V from either leg to ground. It'll just be the ground at the
electrode in your yard rather than the ground at the transformer on the
pole.