Well, that depends on the extent of the french-bavarian victory.
Blennheim by itself was not a decisive victory.
The victories of Marlborough at Ramillies and of Prince Eugene at the siege of Turin were more important.
Now if you have a french-bavarian victory at Blennheim were the opposite army is crushed and Marlborough and Eugene put out of the game (prisoners or killed or disgraced), thisz could change the course of the war but not very much its result.
This war was a war of attrition. The point is that in your scheme, France could keep control of the spanish low countries, decisively defeat the United Provinces, and take control of Piedmont-Savoie.
But in the end, they would have to negotiate a global peace. They would just have a better hand to do so.