> Is there any group of people they won't co-op to keep control?
No
Under senate rules if the chair of a committee is unavailable then the ranking member takes over. Mitchy chairs the Senate rules committee. The ranking member is Alex Padilla.
Correction from digging a bit deeper:
Senate Rule XXVI, paragraph 3—which governs all Senate committees—states:
"In the absence of the committee chair at any committee meeting, the next ranking member of the majority party shall preside."
which in the case of the senate rules committee means Deb Fischer of Nebraska would preside if Mitch is absent, not Padilla.
It is possible that the Senate Rules committee has it's own rule in this regard (they don't publish their rules) but I think that is unlikely.