Maybe Cristiano Ronaldo doesn't need any trophies in our opinions. But I don't think that he is sharing the same opinion now. Ronaldo is always a tenacious player and he would like to continue to play for a team that are competing in the Champions League. If Manchester United can't qualify for it, then he might be likely to leave in the summer for example. Unless he decides to chill at a completely different team, he would continue to play for that kind of teams.
Ronaldo has already said he will stay at United even if they fail to qualify for the Champions League. United is more than just another club for him, so I don't think he will change his mind. Given his age, there is a possibility that we will not see Ronaldo in the Champions League anymore, but I agree with his decision. Let him finish his "big" career at United, and in retirement it will be possible to play in America or somewhere else.
It is great for Manchester United in that case. Because I'm pretty sure that they wouldn't like to see Ronaldo leaving already now. His contribution to the team during this season has been just incredible and he would still continue to do this next season also. Manchester United still had better add a top striker to the team now but Ronaldo wouldn't be in the subs then of course. They would find a formula for it not to create a problem suddenly. Ronaldo must be enjoying to play here then by the way.