There is no (statutory/regulatory) legal basis at all for claiming that a department, chair, faculty member or other individuals must "back off" in the face of a Title IX claim. However, the chair and department could face civil liability for violating the rights of the accused (depending on what the action taken was). This assume that there is no university rule mandating "backing off" – violating university rules may have consequences.
The possibility of civil consequences arises if the university (via the department or the chair) violates their contract with the accused, by penalizing the person contrary to the terms of the contract (look for the grievance clause). However, academic units are usually set up in such a way that "the department" can't do anything, but the chair can, perhaps following a vote of the faculty. The faculty could denounce the accused, but as long as they didn't cross the line to defamation they can express themselves as they see fit. The chair, on the other hand, probably has the power to actually punish the accused, and would need to back off somewhat. For example, the faculty might wish to impose a substantive sanction, but they almost certainly don't have the power to do so, whereas the chair probably does. So the chair needs to check that his actions, as The administrative officer in the department acting as the agent of the university, do not constitute breach of contract w.r.t. the accused.