Specifically, the problem at Real Madrid is that Vini Jr. is the strongest left winger so far and, with his age still very productive, it would be quite difficult for Real Madrid to let him go. Although, when they saw the offer from the Saudi club, it was truly amazing. However, Vini Jr. himself has stated that he still wants to stay at Real Madrid,
Yes, if Real Madrid sells Vinicius, I'm very confident their performance will be poor, perhaps even worse than last season. So, I don't think Real Madrid should be tempted by big offers from Saudi Arabian League teams. They should prioritize their performance and the goals they want to achieve next season. Moreover, they've just brought in a new coach, so to keep him busy developing a solid strategy, key players like Vinicius shouldn't be sold. However, I'm confident Real Madrid won't sell Vinicius, especially as we know he wants to stay at Real Madrid for now. So, given this, Real Madrid will definitely keep Vinicius.
Yes, although his performance last season was quite down and not as good or optimal as the previous season, that doesn't mean he's no longer good; he's still excellent. And most importantly, as you said, he's with Xabi right now. And Vini Jr. is one of the key players already on Xabi's roster. So, there's no compelling reason for Vini Jr. or Real Madrid to sell him.
The 2025/2026 Champions League season will be much tougher and more difficult. It's not just one, two, or three clubs now. But now, there are many top clubs who are very strong and trying to perform as brilliantly as they can, especially in the UCL. So, Real Madrid must be more aware of this and use their best skills to face every challenge, not to miss so many chances like in previous seasons again.