With Messi contribution at PSG clearly having a big impact, it is possible that his contract will be extended. It is not difficult for a PSG manager who has a lot of money on the condition that Messi can strengthen PSG's front position again. I know PSG still has Neymar and Mbappe will continue. Messi's help up front shows that PSG needs him in the long term. It will still happen if the other options i.e. Messi are not extended, the advantage is at Barcelona and what Xavi hopes to happen is Messi's return to the atmosphere of El Barca.
I wonder what indicators you used to determine the extent of Messi's influence on PSG's game? In fact he doesn't show anything above average - PSG dominate Ligue 1 and any attacking player in midfield will have a good goal/assist statistic. Even if you compare him directly with Lewandowski, I would say that Lewandowski shows a much better productivity in Barcelona (although again you have to wait for games against strong teams).
Messi is not the main striker in PSG now. So it is foolish to think that he will score a lot of goals. Galtier changed Messi's position. Now I think Messi's main responsibility is to strengthen the bonding between the midfield and forward players. Messi can now be considered a playmaker. And Messi has been able to adapt to the new position quite well. And I think we will see better performances from Messi in the future.