His career wouldn't be over with a loss but if you keep losing then it is tough to sell someone as larger than life and a mega-star.
Shane McMahon wanted to buy the UFC in 2001, wanted to buy Strikeforce in 2011 and Bellator at one point as well. And Vince McMahon supposedly said to him that the whole model is unsustainable because you can't control who wins. Very tough to build stars when you can't control the outcome.
It's a little easier to do in boxing because it's a much lower variance sport but MMA it is tough. Someone like McGregor comes along, starts KO'ing people to win titles and is the biggest thing the sport has seen, but then just a year later someone is probably already better than him. So where do you go from there?
And the type of guys who tend to win for awhile are guys who fight low variance, unexciting fights. Not dynamic knockout artists but guys like Bones/DC/Khabib/GSP.
