Don't understand this even from a business standpoint, Mayweather at least had the novelty. McGregor cannot afford making his brand look even worse, he will get obliterated by a round 3 nasty KO. He will not make as much as he did against Mayweather, legitimately suffer chin damage and his future asking power will diminish a bit in mma even.
He should just fight mid tier bums like cowboy to get his mystique back, it will make him more in the long run.
If he finally wants to retire, he should fight Canelo as he is the hotness right now. More money to ride off on after a complete destruction, but after seeing kovalev get KTFO he may legitimately be scared of that fight.