Also, Redbull and AlhpaTauri when they signed a contract with F1 They did till 2025.
So for absurd if They can't find an engine They can't leave the F1.
I think they will end with Renault or they will buy the department from Honda I can't see any other solution.
For sure They don't want this Ferrari engine (next year who knows) and for sure Mercedes does not want to sell the best engine to a strong competitor.
Also, Domenicali can't impose the same engine to every team, Ferrari for example will never use a Mercedes engine for obvious marketing problems.
I don't know the regulation, certainly Domenicali can't impose the same engine on everyone, but it could force mercedes to give the engines to the redbull.
I have no idea of the costs for red bull to buy the honda division and continue developing the engines, but if Mateschitz decides to make this investment, then he wants to get back to winning in a short time