Its impossible to predict!
I think you're looking for a gotcha moment, but I've never been arguing that brown is awesome or that he'd hold the job indefinitely.
Brown earned the starting gig in training camp because he was the best overall back. Henderson and akers didn't get much time to emerge as the clear 1, and browm was good enough at everything to lead the team early, as expected.
Brown got hurt and Henderson played well, but when Brown came back, he stepped back into the majority of the snaps for the same reason he had it before - he was good enough all around to have a role.
Henderson has outplayed brown when he touches the ball, and has earned more time, while brown is apparently still the better pass protector. We known his because Henderson got 32 snaps to brown's 28, and akers got one snap/zero touches. Yet Henderson had more than twice as many touches as brown. Which also means that henderson touched the ball on almost half his snaps, not counting pass routes where he wasnt targeted.. which means that when he comes in, the defense will get tipped off that he's likely to touch the ball, until or unless he gets better at blocking and route running.
This seems to be going the route of Aaron Jones vs Jamaal Williams, but I'm not sure if Henderson is as good (or the offense is as good) as Jones and green bay. It's also confused by akers. But it seems like mcvay is doing exactly what makes sense to him based on what he's seen from the players, and he's telling us that henderson is the better runner/receiver but not ready to be a full time player yet.
If we see his snap count go up relative to brown, he will likely take off. If we see akers start to get more snaps, it probably means they aren't sold on Henderson enough to commit long term. Because right now, they seem to want brown to stay oh the field because the other two can't, and they see henderson and akers as better runners than him, and Henderson is ahead of akers. But if akers gets a chance to get more touches, it probably won't be at brown's expense unless Henderson or akers are suddenly picking up work brown would normally have been asked to do. But if we see akers start to get more snaps while brown stays close to half, it probably means he's auditioning for Henderson's role.
So I think the situation is still fluid, and has evolved since training camp but I'm not quite willing to commit to Henderson.