If there was no Xavi, maybe Barcelona would have fallen even deeper. We can see that when Xavi first arrived, he handled the Barcelona team which was already in a very bad state with all the problems they were facing, but slowly Xavi built this team with adequate finances provided by the team management.
It sounds very strange if Xavi is blamed for the decline in Barcelona's performance this season, the team management must actually be responsible because they did not provide full support for Xavi to build this team.
At the end of the season Xavi has decided to leave the team and I think that will make Barcelona very difficult and I think with their new coach next season they will not have a large percentage to be better than this season, I am very pessimistic about that.
Xavi has indeed succeeded in bringing change to Barcelona, where when he first coached Barcelona, Barcelona was in a financial crisis. But he was able to bring in quality players like Lewandowksi and also presented a trophy for Barcelona in his first season as Barcelona coach. But for various reasons he will choose to resign at the end of this season and of course this will be a big worry if the next coach is unable to show his skills in bringing Barcelona to become champions.
Xavi also still has the opportunity to bring Barcelona to become champions this season but with the caveat that he must bring Barcelona to victory in all the remaining matches this season. Indeed, if you look at the players, of course there are several players who are injured and one of them is Gavi, who has had to be absent for a long time. For this reason, Barcelona must be able to perform better if they want to be crowned champions and they must also hope that Real Madrid will lose points in the remaining matches this season.