lost all video and switch control. A doorbell cam, Wyze, cam 2, and 2 Wyze Plug 2 CFH. They have been off for greater than a month. Today the all came back on line.
They are in an unoccupied house. I could check the Modem(online) could not check the router.
What could have happened to cause them to go offline for so long and then all come back online?
Hard to say, but your router could have frozen up and a power blip finally caused it to reboot, just a guess.
If it is an unoccupied location that you aren’t at much, you might want to use a smart plug or timer to schedule a reboot of the modem and router once a week or something like that.
Worth noting too, if you go the smart plug route, you have to make sure it is one that stores the schedule locally in the plug and doesn’t rely on the internet, otherwise you could possibly end up in the same situation if the router locks up. @carverofchoice and/or @Seapup might know a few off the top of their head that work this way?
However it may be easier and more reliable to just get a “dumb” digital timer. The digital ones are better as the off and on is much “cleaner” than the analog ones and much less risk of damaging equipment. Basically use the same relay mechanism that a smart plug does.
What comes to my mind is something @habib has mentioned in a few places:
I’ve also seen @ronl4625 mention this:
Since the house is unoccupied, you might also consider using battery backups at least on your modem and router.
My NETGEAR Nighthawk Modem/router has “Anywhere Access”. They state I can reboot from anywhere as long as the power is on since it is cloud based. Never tried it but I might give it a try from my phone app when I am out and about someday. 
Yeah the issue is if the router locks up that won’t help you. I’ve even had consumer routers with a reboot scheduler built into them, which certainly can help prevent a lock up from happening, but if it does happen, that task probably won’t fire.
Now if it is just something like DHCP/DNS that freezes, one of those options may work, but honestly the most fool proof is probably just a digital timer.
Definitely true, though I wonder if in this case that would have actually prevented the “fix” assuming it was resolved by a power outage. Though the initial cause could certainly have also been a very quick blip that froze up the router.
A UPS plus a timer would be a good combo (timer after the UPS, not before).
Thanks All. The power blips are the most likey. A timer will be installed when I get back.