That doesn't get around the fact that only the Senate has the power to declare a vacancy.
Cite? The Constitution is silent on this. It gives the Senate the power to expel a member, but the clause is ambiguous as to whether this is a universal power, or only for punishing misconduct. If universal, then it follows that any Party which gains 67 seats could arbitrarily expel the opposition. It gives the Senate the power to refuse to seat a replacement.
The only references to a vacancy are "if Vacancies happen by Resignation, or otherwise,..." that the State gets to appoint a new Senator, and then the language in the 17th A. All S.D. needs to do is file suit saying that this is a case of vacancy by "otherwise" than resignation: i.e. incapacity.