20+ years from now, people will look back at Mcgregor with the same fondness that people do today for a Prime Ali, especially if he beats Khabib.
He has given us some great performances and soundbytes, despite how controversial he is.
Top level sport "celebrity" has a few tiers. It looks something like this:
Tier 1 (With the exception of a few locations where the sport is simply not on the radar, pretty much everyone in the entire world knows these names and understands what they are associated with):
Ali
Jordan
Ruth
Tyson
Pele
Hulk Hogan (I know, I know...)
Gretzky
(we might think of another one or two, but not many)
Tier 2 (With the exception of a few locations where the sport is simply not on the radar, the name rings a bell for most people in the world, but they might have a little trouble describing why):
DiMaggio
Mays
Aaron
Mayweather
Foreman
Frazier
Lemieux
Crosby
Johnson
Shaq
James
Rousey (sorry, but it's true)
McEnroe
Bolt
Lewis
Phelps
Rice
Montana
Brady
(and we could think of some others, I'm sure)
Tier 3 (Most people who know a little about the sport and/or know someone who follows the sport will somewhat know the name, and a lot of others will be able to place the name if you offer an explanatory sentence or two):
People like, but not limited to...
Sanders (B and D)
Marino
Favre
Bird
Bryant
Doc J
Mantle
Maris
Williams
Beckham
Ronaldo
Messi
Howe
Richard
Orr
GSP (my perception here may be off, since I'm Canadian)
Silva
Conor (sorry)
Conor is near the top of the Tier 3 category overall, is definitely the top MMA fighter in this category, and is certainly stepping on the boundary of Tier 2, but use his name just among the general public and there will be a number of people who don't know who you're talking about unless some context is provided.