Either way, USSR had their chance at re-conquest, and they failed. They are welcome to try again any time, but they will have to deal with things as they are. Finland aren't even in NATO, they're sitting ducks. So what exactly is holding Russia back? Well, reality, most likely. Finland has an exceptionally large manpower pool of reserve forces, and have landmined the hell out of their borders.
Again, it's a power game, and Finland - using whatever means - out-powered USSR/Russia
As a neighbor, a "brother-folk" and a general supporter of under-dogs, I'm sorry, but you're not gonna see much other than support for them, from me