It's better for him still stay at manchester united. Leaving MU to the another club didn't mean if he can get a better club. So many big clubs have been rejecting him. He must learn a lesson from there. As long as he will be actively playing for MU and why not? it's better rather than try to be a subtitution only for the another club. He also tried to bring MU to the champion league next season.
Ronaldo should remain in Manchester United regardless of their absence in the UEFA Champions league. He is no longer in the top class like he used to be and he is getting old. He needs a club like Manchester United where he would be respected and given the right treatment he deserves. He should not forget the hostile treatment he received from Juventus when the club failed to make it to the Champions league finals. With a new coach and their new signings Man U might make it to the Champions league next season.
When the club's door is not open to Ronaldo, then here the choice is indeed only one to survive and do as usual by playing optimally. But again it's about the ambition of the megastar for the Champions League. If forced, I'm not sure just because pushing myself for an ambition that is not built from team cohesiveness will lead to chaos. That reason is one of the factors why Ronaldo is rejected by many clubs. He's ambitious but the coach can't control him.
If Ronaldo continues to force himself to leave, it is still not certain that he will land at a giant club in a short time.