I'm not as familiar with MMA (though I've watched bouts on several occasions), but I'm from a family of people who boxed (father was a professional boxer; albeit a long time ago LOL) and I also boxed. I can't tell you how many times I've seen a guy hit the ropes like that without the ref stepping in and, when he does, it's to stop the fight. In fact, that's what it looked like he was doing. Now I'm sure what actually happened has happened before, but I don't really recall it. If the guy is defenseless, you stop it. If he's not, it continues until he hits the canvas or the ref steps in to stop the punishment. In the latter case, the fight is over.
Like I said, I'm sure standing 8s have happened in the pros, but I can't remember seeing one. In fact, I "think" there was a rule change with regard to standing 8s.
EDIT: Here it is....
The Association of Boxing Commissions later eliminated the standing eight count in 1998 and it is usually not invoked in professional bouts today. A standing eight count is different from a mandatory eight count, which is only assessed once a fighter is knocked down.
Generally speaking, the ref will give the champ defending his title a little more leeway before stopping the fight, but a standing 8 in a championship fight is pretty ridiculous. Had it been the other way around, that fight is stopped (IMO.....we'll never really know). This was a gift by the ref to Fury.