Technically it is not a force play at all, but a time play.
If the runner left the base prior to contact, then if the ball beats him back to the bag, he's out with or without the fielder applying a tag.
The only thing I can think of as to a tag being necessary would be if the runner had either not left the bag until after contact, or if he had otherwise retouched after contact. In that situation a tag would be necessary even if he decided to return to first instead of trying to advance.