How much would the industry change if MSFT/Sony left?

[MoHasanie]

If they both left it would be a huge change to the industry, but if one of them left, then I don't think it will be too significant. We'd just see a more dominant console. With the lower competition,perhaps we would see less innovation from the one who continues to stay in the industry.
As for the gaming developers owned by them, wouldn't MS/Sony just sell them off?