Yes, it stinks that Democrats came up a bit short, but remember that these were districts held by Republicans who had won when Obama won in 2008.
That said, could this loss actually make Walker more vulnerable to recall?
The way I see it, if the Democrats had succeeded in flipping the Senate chamber, Walker would then be able to point and say, "See, they can stop legislation. So what's the point of removing me from office?" [Of course, I admit that would require that Walker be more than just a pliant tool of the Koch brothers, but that's a separate issue.]
Now, though, the Democrats have a simple message: "If you want Wisconsin back, recall Scott Walker." And given how close the Dems came in Republican-held districts, and Walker's lack of popularity, I think that could definitely be a winning message.