Messi has a close relationship with Barcelona so he doesn't really care about money in order to stay in Barcelona. Likewise with Barcelona, In order to keep Messi, they have to be prepared for the club's financial problems, even though Messi's salary is cut by 50% Barcelona will still exceed their cap. For that, there must be some players to sell or loaned to another club so their expenditures can be reduced and their players (including Messi) can be registered during the new season.
No matter how things are,I still believe this will be sorted out between the two parties,and Messi will still be a Barca player next season.He has been good to the team undoubtedly,and his good relationship with Barca he cannot dent.Instead,Barca will let other players leave,and retain the unique services of Messi,because they know next season is even going to be tougher considering the rate at which top teams are signing players,and won't let there own best player leave.
Most people believe that, Barcelona wouldn't want to upset the best legacy player they have ever had, don't get me wrong Barcelona had many good players in it is history, few even played with Messi, but nobody can deny that Messi has been the best player that ever played in Barcelona and this dude has been there for over 20 years if you include youth years.
So we are talking about someone that is both the best player ever, and also a long standing relationship at the same time. All of this combined would definitely make anyone believe that we are going to see Messi back in Barcelona, but that is "most probably" it is not guaranteed.
If everything was so great then he would have signed a contract already, he wouldn't have waited for this much and let it go to a situation where he is free agent right now. Which means there could be a small chance he may leave, not a huge chance, but not zero neither.