This is the right call - but ultimately since a Manchin run was always somewhat unlikely and now he's ruled it out, WV Dems must now to pick a top-notch candidate. They must hold the governorship at all costs - imagine the shenanigans the state GOP will get involved in if they have everything. Manchin must help to the utmost amount necessary to make this feasible.
Even with a Democratic governor the Republicans in the legislature can do everything they want. They need only a simple majority to override vetoes.
Then why haven't they passed right to work yet? They must have at least one pro-union R in the 18R/16D state senate?