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.
There is no top-notch candidate to hold the seat from what I have heard. Though to be fair, Democrats haven't really don't a great job running the state, considering that its quality of life is Alabama and Mississippi levels of bad.