The same thing that happens if the SSH daemon dies, I guess?
FWIW, I’ve been using Wireguard for a while (probably ~2 years?) as an always-on VPN for multiple mobile devices, and also as a reverse tunnel to pinhole service access inside a LAN. The Wireguard config and daemon has been rock solid. The only time it’s failed is when I messed up the AllowedIPs, but that failure occurs at configuration time. It has never crashed, or stopped routing traffic correctly, or otherwise failed in a way that interrupted traffic flows.
I have 5 locations running effectively independent VPNs, each hub connected to each other for redundancy if a VPN falls over.
i.e. Each hub has 1 VPN in, or is connecting 4 ways out.
If the port forwarding or something fails inbound, then I can connect via another VPN and try and debug/diagnose what is wrong.
If all VPNs are reporting down, then I know the pi/internet is completely down. It will either restart connectivity, but I have someone there who can plug/unplug/restore the system if necessary. The same kind of problem would occur if ssh falls over or wireguard.
FWIW, I’ve been using Wireguard for a while (probably ~2 years?) as an always-on VPN for multiple mobile devices, and also as a reverse tunnel to pinhole service access inside a LAN. The Wireguard config and daemon has been rock solid. The only time it’s failed is when I messed up the AllowedIPs, but that failure occurs at configuration time. It has never crashed, or stopped routing traffic correctly, or otherwise failed in a way that interrupted traffic flows.