You can't possibly decide yet because Realmadrid might eventually lose form which might give the advantage of Barcelona overtaking them but at the same time the chance of this prediction is still somehow slim.
Barcelona in their last few matches had winnings alot of winning s which is a very good sign of then gaining and holding firmly to their ground , although it was a bit late, it was after the announcement from Xavi that they picked up a good form and good game play and I don't think that will still stop him from leaving the club but I wouldn't be surprised if he still wish to stay at the end (it's decision)
In next Sunday's match, Monday to be precise, both teams will certainly show their best performance. Especially Barcelona will go all out to reduce their point difference in the standings. Yes, Barcelona in the last few weeks has shown that their game has improved quite a bit. I see that there are only a few weeks left for this year's league to end. In this El Classico match, Barcelona must beat Real Madrid. If Barcelona loses or draws in the match, I think it will be much more difficult to catch up on their point difference.
If we talk about predictions and opportunities, Barcelona certainly still has the opportunity to overtake Real Madrid at the top of the standings. But as you say, that chance is very small. The reason is that currently Barcelona is 8 points behind Real Madrid. In my opinion, the point difference could be said to be very large. So in a situation like this, there is a simple scheme for Barcelona to shift Real Madrid's current position, in essence Real Madrid must suffer a minimum of 3 defeats in the remaining matches at this time (in La Liga). Meanwhile, in my personal opinion, it would be very difficult for Real Madrid to lose, especially three times. The reason is, the teams that Real Madrid will face in the remaining matches this season can be said to not be very strong. Perhaps only Barcelona can be said to be the strongest team of all the teams that Real Madrid will face in the remaining matches this season. Even that is not a strong guarantee that Real Madrid can be beaten.
Although Barcelona's performance is currently improving again. However, I don't think that's enough to beat Real Madrid, who always perform well in La Liga. Apart from that, for example, Barcelona was able to beat Real Madrid and the point difference was getting closer to Real Madrid. However, this would be useless if for example after that Real Madrid continued to win in every match. Because as I said, the tough opponent that Real Madrid will face in the remaining matches in Laliga is only Barcelona. And the remaining matches are against other teams, it is very likely that Real Madrid can definitely win the remaining matches. So in essence, Barcelona's opportunity to overtake Real Madrid at the top of the standings will certainly be very difficult.
And regarding Xavi, I think it is very likely that he will still leave Barcelona at the end of this season. Even though the Barcelona players are currently showing better development. However, I don't think this will make Xavi cancel his plans. The reason is that Xavi must have thought carefully about his decision. That's why Xavi announced his decision several months ago.