Ronaldo is not regretting doing terrible, dude has made 500 million euro total from the 2.5 seasons he played here, why would he be upset about losing, that is not that important. So much so that for the 2.5 seasons he has been here, they have been losing all the time, not getting any better players, and other teams are doing much better, but he agreed to stay one more season in exchange of 180 million euro plus 5% of the club, so he clearly only cares about the money anyways, and why would he care about anything else, it's a job.
Money isn't Ronaldo problems, the problem he has is to be the best regardless of the age that he's clocking. Ronaldo wants to win all trophies in Saudi Arabia but his teammates are letting him down as they're not helping him out. Ronaldo is now too old for him to do it alone but he won't stop until he wins a trophy with Al Nassr and that's a good mentality to have even at this stage that he doesn't have much strength left in him to be able to compete at the top as he used to do when he was still younger. Ronaldo is willing to exchange all the money that he's receiving for a trophy with Al Nassr. You can see the hunger in him to keep winning when he's playing.
I agree with you and just like you I think for a player like Ronaldo considering the money he has, won't lose everything to earn more money, and maybe the main reason for him to join the Saudi League was not money but he joined this League to have more chance to earn the AFC Champions League title since he never achieved anything in Asia it was interesting for him.
But now I think since he is nearly disappointed about achieving any title he is now thinking about maybe leaving Al Nassr because he knows he won't get anything in this team no matter if they get a coach like Pioli.