Since this is in the United forum, we should expect absolutely nothing. We should stick with the decision we have made, instead.
How Ronaldo will perform is irrelevant. Different side and tactics, different opponents and different tournament prerequisites (in terms of pace, physicality/aggression, well-drilled tactics and preparation). He may lack the sharpness, but the intelligence is still there. So, in a team where everybody will be trying to feed him and against opposition who usually lacks the cohesion of club football sides (especially early in the tournament), he may score a few goals. Good for him and for Portugal.
But why should we care? United have invested time and resources in a newly appointed manager. ETH may have a use for a player of Ronaldo's vast experience, but he doesn't seem to see Ronaldo as pivotal to his plans. He will alter and tweak his plan to suit the team's overall abilities better, but he will not build a team around a 37yo poacher who would be gone at the end of the season either way.
By entering this debate, we're doing Ronaldo the biggest favour. In the end, that's what the fuss is all about. That the new regime and the new manager refuse to "kneel and kiss the ring". When that time arrived at Real Madrid, they shipped him swiftly to Turin. Just when the situation was about to reach critical mass at Juventus, Ed and the rest of the gang, who had spent three years rebuilding United on nostalgia and sentimentality, were there to play the role of the useful idiot.
Pogba had a wonderful WC with France. He was even racking up good numbers when he was fit with us. This didn't change the fact that it was extremely difficult for United to build a team around him. Good luck to Ronaldo and to Portugal (who have always been one of the most likeable national teams, IMHO), and, hopefully, a club will require his services in January to help them push for their targets. We move on, and get the forward who will fit our new system best and compliment the existing young attacking options well.