Nope. Wouldn't have let it happen then, and certainly not be entertaining this Floyd/Conor fighting each other in MMA foolishness. "Letting that fight happen" means I'm the boss, and I have the decision-making power, in which case... not on my watch. The UFC dropped the ball by letting a quick short-term cash grab's consequences affect their own brand. I wouldn't have shut down the idea entirely, but used the possibility of it happening as a means to maintain direction and focus.
The UFC and Conor split approximately $100m 70/30, and given Conor's previous earnings and endorsements, he most assuredly is worth $100m. Floyd made hundreds of millions, Conor made about $70m or so, and the UFC pocketed around $30m for a fight they didn't have to promote or advertise, and had no real expenses running against the "windfall". While that may sound like a no-brainer decision to make on the UFC's part, I can help but wonder if Floyd and his camp capitalized on the UFC's lack of foresight and greed.
Given the length of time that has passed since MayMac went down, I can only assume the UFC didn't take enough precautions and impart stipulations to protect their own brand and ensure Conor keeps making them money. Conor riding the pines, and not going elsewhere to fight is keeping him in the UFC's fold, but he's not making them any money.
The $30m was a token amount to Floyd, but it let him essentially take the combat sports' world focus for almost a year and made a whole lot of money doing it. Floyd didn't give one fuck whether or not it caused disarray or had negative consequences on the MMA organization and their top draw post-fight. Floyd training in a cage, showing of TMT 4oz gloves, applying for an MMA license... all of those things put him right back in the forefront of the MMA world, and the UFC is indirectly responsible for that and are more newsworthy than MMA's biggest draw.
Conor fighting Floyd has taken him away from the UFC for about a year and a half so far, which I feel it's safe to say he could have fought 3 times during that duration. In those three fights, the UFC would have made more than $30m and kept their biggest draw and his focus and attention on their brand. Before anyone says "Conor wouldn't have fought Tony or Khabib, he never would have defended... etc", bear in mind the UFC could have orchestrated the validity of Conor fighting any opponent, but at least it would have been under their banner and in their sport.
Any boxing crossover "superfight" should have been used as a means to keep Conor fulfilling his contract with the UFC. There's no doubt eventually Conor was going to try to move on and entertain more lucrative options, but I think the UFC failed in accelerating that goal. Had Conor fought a few more MMA fights and bolstered his highlight reel KO's and ran a longer streak it likely would have led to an even bigger payday for both the UFC and Conor in the crossover fight, and put the UFC in a position where they weren't so dependent on Conor actually returning to the sport.