Nah I dont think it will end up like that, maybe around 85% sure. Cause if we think about it Mikado will probably support Shou and Fu getting together with their own shop.
The only problem here would be if Mikados shop doesnt hire more people or if its in a rut, which could lead to Shou staying with Mikado and your scenarios happening.
I think that's rather unlikely bc it's already proven by the manga itself how calculating Fukusuke is -he knows how Shou values and treasures Mikado bc of all the things he has done and he knows that if he kills Mikado it will only create the opposite effect. Shou will hate him and really try to get away from him not only is it because he committed murder but to his poor precious Mikado-san
This is all my own thoughts on the matter.
I have this really bad feeling that Fukusuke ends up killing or seriously hurting Mikado-San. We've accomplished to prove the point that Fukusuke is a sociopath and willing to hurt anyone in his way. He wants Shou-kun to follow him when he makes his own shop, but Shou is dedicated to Mikado and headstrong. So, in order for Fukusuke to get Shou to come that means that Mikado needs to be out of commission ie; shop get's ruined, he dies, or something major happens that either makes him turn his back on Shou. Maybe Fukusuke ends up blackmailing Mikado, or as shown before Fukusuke isn't above framing him and making Shou believe that Mikado is a bad person.
We'll find out though, huh. I'm looking forward to the next update ヾ(❀╹◡╹)ノ~