If Google isn't making enough money off of Stadia to justify its continued existence, I doubt they will invest in buying out some notable third-party company (assuming any of them even want to be bought out). They will most likely just shut it down like they've done with so many other services they've provided in the past. And the immediate impact of that would be felt strongest by gamers who actually did invest time and money into Stadia. They would lose everything as they owned nothing, with not even locally saved digital copies of their games to show for it. The games simply vanish forever.
Google stated they don't plan on buying any company or exclusivity like Epic is doing. They are oppening their own first party studios. The first of them was opened in Monteal some days ago. And Google doesn't care if it will take years until we can se a big AAA 1st party title either. They plan to give Stadia support for at least until 2030.