In Avengers: Endgame, Thor goes back in time to extract the Reality Stone from Jame Foster, but when he does so, he also summons Mjolnir and takes it with him. Does that mean that the Thor in that timeline doesn't have his hammer?
When Steve goes back through time to return the various stones (including the one that's going back to Asgard) he takes Mjolnir with him. It seems highly likely that the goal was to return it to its appropriate place in time.
Per the film script.
BUCKY BARNES (CONT'D): Gonna miss you, buddy.
STEVE: It’s going to be okay, Buck.
[Steve picks up Mjolnir and takes his place on the platform.]
[SAM LOOKS TO SMART HULK AT THE CONSOLE.]