Piston engines are flown all over Canada at temps below -30. You just need to care for them after shutdown (engine covers and heaters etc).
Yep, otherwise shutdown for the winter. Doesn't work if you are in it as a viable business. I have lots of hours in SE at -40. You do need some local knowledge and a properly modified aircraft. Beyond that it is fun; there is nothing like the raucous snap of a C-180 or 206 two blade prop on takeoff at -40! And the increased performance is a real thrill.
First guess is their engine breathers froze and blew out the oil.
Second is fuel blockage from water in fuel. There are some preventative measures for that which I won't discuss.