I think the 2022 world cup will be the last world cup for some football stars, not only messi and ronaldo but pepe, modric, di maria and maybe even lewandowski and muller also have the potential to retire, some of these players are now entering the end of their careers in the national team and of course the regeneration of players will make countries competing in the world cup better than continuing to rely on old players, indeed their performance in playing is still very good but sometimes age is an important factor to be considered by national coaches.
Dont know if Messi will be retire after that world cup , but ronaldo, pepe and modric they will be to 80% !
About Müller its maybe the same as Messi and he will be making a few years till its the time for say good by to the National Team.
The old players are needed sometimes for the team spirit.
I think on Facebook I saw that Messi has stated he wants to play in the next world cup also. I don't know if that is true but it would be something to watch Messi play in the next world cup as well.
But except for Messi, I think for the others it is going to be the last world cup. Especially for Ronaldo. And that's why I really want to see a good performance from him in this world cup.