Vinicius should be fine at Real Madrid, he will probably stay there at least for another 5 years, shouldn't really be a problem. He needs to learn to live with Mbappe though, because Mbappe is a great player too, and together they can be amazing.
However, so far they are cancelling each other out, instead of helping each other be better. Which is why many people see a problem with this. I am guessing that it is going to be an issue that they can't handle for the short term, which is why they need to handle this as quickly as possible. We can't really consider this to be an easy solution, they need to get those two together and tell them to play nice and get them to like each other and play well together to make this happen.
Vinicius contract expires in 2027, but I think Real Madrid will try to keep him at the club for longer by offering him a new deal.
Vinicius position in the squad seems irreplaceable, even though he hasn't yet established a good chemistry with Mbappe. I think, over time, the two players will be able to form a good connection up front, as both possess above average individual qualities. Xabi Alonso will certainly try to address this issue, and I think he has the ability to do so.