My car was stolen and I have it returned now. Tire is missing and the rim is probably damaged. Will I have to get a new rim?

Depends on the damge, sorry this is something only an expert at a tire shop can tell you from the amount of damage. Some rims can be reshaped slightly and in the end even if it is close the only way to know for sure is to try and put a tire on it and see if it holds.

But if the damage is seroius enough yes you will have to

Take the rim to a tire shop they will put it on their balance machine and determine if it's
Bent. If it's even slightly bent it will cause alignment issues and uneven tire wear to occur. Junk it and pick up a good one from a parts/salvage yard for cheap.