I don't know if it will be a good idea for Lionel Messi to get back to Barcelona. After all, what Barcelona is doing right now cannot be a good procedure going into the future. These old TV rights bring in players who are way too expensive for their age. But on the brighter side, Barcelona is doing well, at least in La Liga. The thing is if Lionel Messi comes back, he will have a lot more competition. But I really don't believe he is going to come back. At this age, it's better for him to stay in PSG and take those cheques.
I don't know if Cristiano Ronaldo is going to be pursued by Chelsea. After all, he is not having a good time at all at Manchester United. It is always a gamble to bring in a player who is not in form. It will obviously be very good for Cristiano Ronaldo if he can go to Chelsea. I want him to at least get out of Manchester United and go to another team which he will play in the Champions League at least.
I don't have an answer to your question regarding Messi's return to Barcelona. but if that happens, it looks like Messi will not play full time and he will most likely end his career at Barcelona. maybe one season is enough for him, regarding the salary issue, I think maybe it can be negotiated. at least, we can only speculate about the rumors of Messi's return to Barcelona.
I'm not sure if Chelsea still have interest in signing Ronaldo in the next transfer window, as you say.
bringing Ronaldo to Chelsea is a gamble which involves signing players who are not at their best. if lucky, Ronaldo can find his rhythm while playing at Chelsea. if he doesn't improve, his fate will be the same as at Man United.
It is really hard for me to realistically think that Lionel Messi will go back to Barcelona. Why would he make things more difficult for himself? If he wants to face some new challenges, that's fine. Otherwise, there is no point in moving to Barcelona right now. And obviously, he will have to take a pay cut if he wants to move to Barcelona. There is no need to do that at this point in his career.
I think Chelsea would be really cautious about bringing Cristiano Ronaldo into the team. In the recent past, they brought in Romelu Lukaku. I think he was brought in for 97 million. That money absolutely went to waste because he did not perform well at all. Cristiano Ronaldo is not going to be so expensive for sure. But are they willing to take that chance?
Cristiano Ronaldo did score in the last match with Manchester United. But is that enough to prove that he will be performing better at Chelsea?