The reason sen fell off was because of tenz..but hear me out.
Not because he's a bad player but he just doesn't fit the need of the team. Ever since he came there have been synergy and role issues. Sick and shaz had to leave their duelist roles and move to supports and the lack of cohesion eventually started showing in their results.
Everything worked well initially because the scene hadn't developed much in the beginning but now the competition's tough. Now they needed some scapegoat to reason with the lacking results so they pinned it on zombs and he got kicked when in reality it wasn't because of him that they were losing.
Players in this team are playing roles that they arent supposed to play and it just shows. I think everyone in sen is good but not good enough to work out together, they would probably find more success splitting and playing for different teams