How exactly could Kobach "force" Democrats to select a replacement? If they decide not to, there's nothing he can do about it. Or perhaps the Democrats could select Kobach, Roberts, Brownback, or Yoder?
I don't think he could. Even if the law mandates that Democrats must select a replacement, the law doesn't give the SOS any recourse if the KS Democratic Party refuses to do so, and there's almost certainly no penalty under the law for refusing to do so. It sounds like he's talking about trying to go back to court and get a judge to order the party to select a replacement, but the SOS doesn't have standing to bring that suit.
Maybe he could find a member of the state Democratic party that would have standing to bring a suit, but it doesn't seem that there's enough time left for such antics.