If the cliff collapsed, there wouldn't be any reason to animate them slowly beginning to drop before the tree snaps, since the cliff wouldn't first slowly drop before collapsing.

But no, they're shown close up first slowly going down before they actually fall completely. Even though they very clearly shown in the tree snapping cut that there's absolutely no one on the tree. Not that we needed confirmation, since we already saw Nozomi grabbing her from the tree and then bringing her against her chest.

If the cliff collapsed from their combined weight, they would just immediately begin to fall and there should be the cliff rubble coming down alongside the tree stump.

It's an absolutely retarded sequence of events.