There's always a hospital visit or wreck or death that causes them to not be able to pay. 

Our governor is a train wreck.

Your tenant goes in and wrecks the house, steals everything out of it and sells it, and then squats in the home until you evict him.

Meaning - is it possible the tenant was the cause of the surge - and hence - wrecked your furnace?

That said the home is really a wreck (30 yrs as a rehabber/contractor/investor I am).

Wrecking bars/ pry bars.A 4' or 6' ladder.

The OP wants another thirty years max out of this sidewalk, and the house is probably going to go to the wrecking ball just a few years after that.

That way, you can just give 30 days notice to end a tenancy, as well as 30 days notice to change any rules, etc.The things that usually wreck roommate situations is unwanted guests, not cleaning up after themselves, messing with thermostats, stealing food.Some of those things can be pretty easily dealt with - like including a weekly cleaning service in the rent, putting little apartment fridges in the rooms.But, inevitably, there will be a roommate who you will want to get rid of, so having month to month agreements is the easiest way to get rid of them.  

He also told me he changed the locks on the door so she couldn’t come back, and if I try to evict him he will drag it out and wreck the place.

I would say no for 2 reasons:1) she might want to make it into a grow room, which will wreck your unit - the humidity and potential water on the floor, plus the smell, etc., will possibly do major damage; and2) tenants who start wanting to change things are never-ending high maintenance tenants and you're better if they leave.