I'd say that yes, Kander did prove MO isn't lost for Dems. Kander just couldn't overcome Trump's doubled-from-2012 margin. MO has a lot of swing voters who have begun to consistently vote GOP for president, but are willing to vote DEM for most statewide offices.
I'd say so. Sometimes, there is a limit to how much a downballot candidate can outrun the top of the ticket, even in states that have a track record of splitting their tickets. I really think if Clinton had only lost MO by 2012 margins, Kander and maybe even Koster would have won.