Is it obligatory to return the Mus'haf and its bearer to its non-Sunni owner after the relationship has ended, or is it permissible to place them in a mosque?

The Mushaf (copy of the Qur'an) and its stand must be returned to their owner. One's obligation is not fulfilled except by returning them to her, as long as her location is known and she can be reached. It is advisable not to sever ties with her and to try to guide her to the Sunnah with wisdom and good counsel. If the questioner cannot do this herself, she should seek help from others and present her with books and tapes that encourage adherence to the Sunnah and warn against innovation.