Why did your wifi went down ?
Some wifi and zigbee are on the same wavelength, if someone was jamming it (this is illegal), both can be taken down like this.
So if my internet goes down because there's an area fault, I can't, for example, scream movies from my NAS, because the router just refuses all connections. It's infuriating. Especially as the local Internet drops constantly due Virgin selling over capacity.
Is it worth it to double-NAT, and run a router between your internal network and their internet box? Then your router is doing the internal routing and possibly DNS too. It’s not perfect, but it might be worth it if the internet drops that much.