My principal doubt is, if Girona after this international break is gonna still being this good, or they are gonna start to fall behind, maybe they can last until the winter break, and become the winter champions

i remember the alst team becoming winter champion asides of the big threes was Real Sociedad a lot of time ago.
Of course, it's not just you who doubts Girona, but many people besides you are pessimistic about Girona. I personally also doubt that Girona will maintain its performance until the end of the year, but Girona has good motivation and self-confidence to maintain its path. Girona have two difficult games left until the end of the year, namely against Bilbao and also Barcelona in the second week of December.
It is feared that Girona will lose points against Bilbao in the next match, but considering that Girona is playing at home, they have good spirit and confidence to win the match. If Girona can maintain their form until the first half of this season is over, then I am sure they can advance to the Champions League next season.