Earlier quoted context omitted.
Highly unlikely, since I presume all car windows would have been closed (winter in Finland is COLD) and they would have been strapped in with seatbelts. It's difficult to escape from a submerged car even in the best of circumstances, and being suddenly plunged into near-freezing water in the black of night is far from that.
While your reply is interesting to me, what I actually was asking was, "if these people died in circumstances that did NOT involve a car, but in the water, would the bodies have been found eventually because they float to the surface?"
Apparently bodies sink initially, float temporarily for a while due to bloating, then return to the bottom again after some decomposition. So you could easily miss the window if there are not good conditions to beach it I guess?