Yes sometimes it's possible to free or unseize an engine that seized up because of no oil.
I once had an oil leak before that drained all my oil all of a sudden while going down the road and then my engine seized up as a result.
I thought the engine was ruined but I tore the engine down to the heads and removed the oil pan and replaced all the main bearings in the engine and I soaked the pistons with some Marvel Mystery Oil overnight.
Then I used a 2x4 piece of wood and a small sledge hammer to hit the board with to force the piston down which helped them become unstuck.
I hit each piston slowly until they all started moving freely.
Sometimes it's just the friction that causes the pistons to stick and sometimes it's the main bearings freezing up due to lack of lubrication.
So sometimes an engine can be fixed that is seized without rebuilding the entire engine but sometimes it requires a complete tear down and rebuild of all parts.