Look, without teleportation, which is neither scientific, nor has any explanation in the series, moving through physical space takes time. Regardless of how fast you are moving, moving, through space, takes time. There's a reason we measure speed in units of distance/time. I know this is just going to be dismissed as conjecture, but I'm saying it anyway: for Jiren to be frozen in time, ie entirely immobilized via time, he would have to be unable to cross any amount of distance by virtue of being unable to interact with time. That's the only way that works. I have no idea how the DBS writing team
thinks Hit's
Time Stop ability worked in the episode, but, scientifically, that's the only way such a feat should be able to work. As such, no, destroying the stage beneath Jiren's feet wouldn't have caused him to fall out of the ring unless Hit released him from Time Prison. Again, Jiren could not have fallen if time is not flowing for him, because there cannot be any movement without any time. The stage could be obliterated, the pieces of it would fall down, all of which takes place over the course of a few seconds - a few seconds which Jiren, by virtue of being imprisoned by time,
does not actually experience. To Jiren, those seconds simply don't pass. Even though there's nothing for him to stand on, Jiren doesn't fall, because, without Time, he can't. If Cabba, Caulifla, and Kale
did destroy the floor underneath Jiren's feet, and Hit
did release Jiren from Time Prison, then Jiren would be free to catch himself before he fell into the void, which, sure as you're born, Jiren would do. Even if they eradicated a whole swathe of the arena, no small feat, so that no portion of it was within Jiren's reach as he was released from Time Prison, Jiren would be free to do what Krillin did when saving 18, blast himself back onto the arena. There's simply no way Jiren was going out that way.
Now, actually, I can think of another way Hit's Time Prison ability might work. It was stated that he was essentially using his Time Skip offensively, causing Jiren to skip time, instead of himself. The only way that makes any sense is if Hit were causing Jiren to skip time backwards. Hit, using his Time Skip, skips through time so that his actions happen faster than they should by cutting seconds out here and there from the total time it would take him to perform an action. I don't know how it works, but that's what it seems to do as far as I can tell. So, then, what seemed to be happening was Hit was continually causing Jiren to skip that first second of his movement, placing him
back, rather than ahead, to the instant before he began moving. How this operates, in terms of physics, is... a bit more fuzzy. In this case Jiren is not necessarily frozen in time, he is simply... not moving. He is continually in a state of being just about to move. The time in which he would move is still "happening," but over and over it is being reset to "not having happened
yet." What this seems to suggest to me is that, again, while Hit is maintaining this effect, any attempt to move Jiren through gravity will likewise be skipped and reset to Jiren "not having fallen yet," unless, of course, Hit releases Jiren from the effect, but, as stated above, if he did that it is obvious to me that Jiren would catch himself or in some other way simply
not ring out because of falling.