Would have been quite the paycut. I imagine the only reason he didn't take it earlier is because he assumed he would see out the season at United, perhaps one more and then still go there for the same money.
To put it into perspective, At United he was earning about £30m after tax. In Saudi he will be earning, from what I can tell roughly £177m per year after tax. Thats insane. Do I think he will regret it? Yes, absolutely. He doesn't need that money and he will be remembered poorly by many after his antics over the past year or so.