Real Madrid can replace Vin Jr if they want, but they will need a good and reliable right winger before they can let him go so that Mbappe will go back to his natural position which is the same position with Vini Jr, then should look for a reliable striker that can score plenty goals like Haaland.
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, even though the Saudi club remains adamant about getting their hands on the main player. They are even preparing a €350 million offer.
Source: BREAKING: Saudi Arabia are ready to make a €350M offer to Real Madrid for Vini Jr
Furthermore, regarding Mbappé's current position as a center-forward at Real Madrid, I think Mbappé has adapted quite well and just needs a few adjustments. So, with that in mind, I don't think Real Madrid need to bother replacing Vinicius with Mbappe, let alone selling him. I think Vinicius is a winger who fits perfectly at Real Madrid, so even replacing him with Mbappe wouldn't be as good as Vinicius. The proof is that Vinicius and his teammates at Real Madrid have already won many trophies, including the Champions League trophy. So, with that in mind, Real Madrid must remain committed to keeping Vinicius. Because in my opinion, he's a truly great footballer, albeit a bit egotistical.
The current situation of Real Madrid is very bad. After a trophyless season, there is a feeling of dissatisfaction among the team's players. There is a lot of discussion among them about the issue of releasing one of the team's forward players. But Vinicius has a contract with Real Madrid until 2027. But when the new contract between Vinicius and Real Madrid came up, Vinicius demanded double the current amount. At that moment, Saudi Arabia made the offer. But Vinicius did not agree to the offer now. He wants to play for Real Madrid.
If we look at Real Madrid, they are very worried about themselves. Without Vinicius, the team will be weak, but Real believes more in reality. Under the new coach, it may be possible to bring in someone new without spending so much money. Since the coach is new, I think everything will be done anew. Real Madrid is going to make an incredible bet on the new coach. As a result, we may not see Vinicius in the team.