Casemiro with his current level of play and fitness is indeed plausible that he is able to continue his contribution at a high level for three more years. He is certainly the most important player for Manchester United, even though we dont see his best performance like he used to perform at Madrid, his impact to the team is so significant. His ability to gather and control the midfield not only showcases his individual skills but also show his importance in the overall team dynamics.
Manchester United being reluctance to sell Casemiro is reasonable with the sentiment that players of his caliber. He is invaluable asset who consistently delivers and fulfills his role effectively. Manchester United as a club, especially during a recovery or rebuilding phase, would likely prioritize retaining such key players who provide stability and leadership. His experience, work ethic, and on-field contributions can serve as a stabilizing force during transitional phases.
We can't be sure about his fitness yet but I can say Casemiro is still at a level in which he can play for more years in top-level teams like Manchester United without problems, however, I think Manchester United should keep Casemiro but even if they don't want to have this palyer any more I think Casemiro can choose to stay in another team in the Euroa which there are obviously many offers for this palyer.
But moving to the Saudi countries is just too soon for a player like Casemiro who can play at this level for his team.
The injury he experienced previously really caused Manchester United to have a less than optimal midfield, even Casemiro, who previously performed well, had to be absent for quite a long time from Ten Hag squad.
There was big loss experienced by Manchester United after Casemiro absence, namely that the front line and defense were unable to play optimally considering that he is midfielder who always provides competitive performance for Manchester United.
But instead of keeping this midfielder, he instead tries to let him go, Ten Hag will really feel a big loss if Casemiro leaves Manchester United and of course PSG is the name associated with Casemiro.
Rumors about PSG having an interest in signing Casemiro have been circulating for some time, but in his current condition it seems that Ten Hag does not want to keep him as Manchester United player.
Moreover, Casemiro is still not that old because he has only just turned 31 years old, plus he can still develop in Europe, so it is unlikely that Casemiro will go to Saudi.
His career in European football is still wide open and this could be an opportunity for Casemiro to get a truly worthy team that can give him the opportunity to win titles in the future.