If your client needs an MCT to associate, then they need an active MCT, otherwise it can't be counted towards their partner certification. So an MCT alumni (which basically means "ex-MCT") will not be valid for them.
The "alumni" program was created as a way to let people who chose to no longer renew their MCT to keep in contact with the program and other MCTs. This program lets members access MCT forums and attend MCT events so that they can keep in contact,
but does not let them take part in MCT-exclusive activities such as teaching public MOC classes, which is the reason that CPLSs need to have MCTs associated.