Usually you will be playing by "one object ball foul OK" rules which most people refer to as "cue ball fouls only". Since you only disturbed one ball -- and presumably no other ball during the shot passed over the spot it had been sitting -- it is not considered a foul. Normally the seated player has the option of putting it back or leaving it where it is. I think that is reasonable here as well, which means the ball could be left where it is but because it was pocketed in an extraneous pocket, spotted on the foot spot at the end of the inning at the choice of the seated player.
Here is a relevant rule from the CSI/BCAPL rules:
If a single disturbed ball falls into a pocket with no effect on the outcome of a shot, your opponent has the restoration option. However, if the disturbed ball is designated by specific game rules as the game winning ball, it must be restored. If the game-winning ball is disturbed and falls into a pocket when there is an effect on the outcome of the shot, it is loss of game.
I think this rule is broken. I doubt that anyone would accept a loss at nine ball for such an accident and if my opponent needs one at one pocket, that ball by the side is possibly his game-winning ball.