Soldato
It's something that I'm surprised Mercedes aren't considering (not necessarily buying them out, but certainly supporting a team like Ferrari do Sauber), but there's been no solid rumours of anything like that. If the Stroll family take over there's no team where Mercedes can send their drivers to learn (hence Ocon's loan to Renault).I don't think that Perez has done himself any favours with regards to future seats over this. Would Mercedes buy them out and run them as a B team maybe? It would be one way to get their young upcoming crivers into seats.
It makes me question whether Mercedes are genuinely in it for the long term ahead of 2021, but chances are they just don't want to invest so much in another team.