I agree with Dude about U.S. Fiat being less bad. Depending where you offshore, you may be jumping from the frying pan to the fire. I'm not trying to politicize the issue here, but no matter where you go, someone who doesn't care anything about laws, will be armed and dangerous in your area, even if they just have machete. Being able to defend yourself becomes very important in collapse situation. If you are going to be with a group, numbers help, but once again an armed thug can control a whole lot of unarmed people. Depending on where you live in the U.S. you may be able to level that field, if you stay. Just a thought here.
As for your mortgage, though. If you think you could sustain the rent level you currently have after a collapse, then keeping it may be a good way to go. If it were me, I would look and see how much equity I have in the place today and decide if I wanted that equity for something else. At 35 years left, I'm guessing you don't have a lot of equity unless the property has appreciated significantly since you bought it. Also you need to think about whether all three units could stay rented while you were being an absentee landlord. In my area $800 U.S. would be moderate rent to pay on "decent" place to live. Decent is a safe neighborhood, with the unit in good repair, or some type system to get thing repaired in a timely manner. $1200 is about the norm for the above requirements. I wouldn't live in my sons duplex $850 a month for example, because of safety issues, but I would his house. $1650 is on the high side, but is common around here.
Hope this helps.