A few things I would have done different. Since you previously filled these meds, you now technically have a working relationship with them. Under circumstances where there’s a controlled substance I’m uncomfortable with, I heavily impress the side effects of long term use, the alternative medications available, and recommend tapering of these. Sometimes it works. If they don’t choose to, I give them one week supply With a UDS, promise to fill the rest when results are in, and encourage them too follow up with their regular provider. I wouldn’t go so far as to educate the other provider as I’m sure they more than understand the reality of addiction with these meds. Some providers just don’t care or don’t want the fight. If you felt inclined to justify to them your choice then maybe.
You’re never obligated to maintain another providers therapy. But you do have some obligation to reduce the risk of withdrawal. With either a tapered dosing or arranging an alternative appointment. By all intents though, this is a patient in a shared clinic. Presuming you and the other provider are mid levels and your previous history treating this patient, you already own their outcomes. You likely won’t be sued at the end of the day though.