Do you think they would be closer like "OH MY GOD YOU ARE BACK !!! LET'S FEDERALIZE AGAIN !!!" or more distant than ever ? Because from what I know (it's only a one person testimony from someone who was a child when the separation between Czechia and Slovakia happened, so correct me if necessary) Czechs and Slovaks, on the contrary of Yugoslavs, were kinda happy together, there was a debate about representation and developpment of Slovakia, but they got along quite nicely.
The main point against it is that in this world, they are never force-fused again after the treason of Czechia by Tiso, so I don't know, what do you think ?