It depends. If, as Maxwell said, his approvals are too low, he won't run. However he may run and lose. When it comes to Governors, its really that "third term inch" rather than a 6 year inch. I suspect he'll have a massively contested and competitive race.
As you're on the ground in WI, who do you think the Democrats would run in 2018 (regardless of Walker seeking reelection)?
People likely to run include Lena Taylor, Peter Barca, Kathleen Falk. Falk probably wouldn't win the nomination, Barca is really just a boring suit and Lena Taylor is insane and could easily turn a Democratic win into a loss, and I suspect she would want to run.
If the Democrats want to win they should nominate someone who might resonate with the rest of the state. They could probably easily win with Abele though he probably couldn't win the nomination with being handed the reigns of MPS and selling all county land except parks and O'Donnell park. County Board is useless and I'm glad they don't have much power anymore (imagine the most useless politicians from both sides in one body and that's what you have) and the teachers union is going crazy over it too, even though they've been worthless and haven't done anything in 20+ years so he's out.
Other people who could probably win and wouldn't be awful would be Jennifer Schilling (D-La Crosse), Kathleen Vinehout (D-Alma), Jon Erpenbach (D-Madison) but they would probably all be long shots.
I suspect Walker doesn't run, and if he doesn't it's going to be a bitter fight between Vos and Fitzgerald.
I followed the whole Bucks situation (being a long-bitter SuperSonics fan and all) and Lena Taylor would be an unmitigated disaster as a Democratic nominee. Abele seems (unfortunately) like the likeliest choice to me, but Wisconsinites obviously know much more about the state's political situation than I.
Could one of the Vos/Fitzgerald pair challenge Baldwin and the other run for Gov?