I also really like the idea of having your lawyer send an "official" letter. It can even be phrased in such a way that "due to current circumstances, your visa has been cancelled..." Passive voice.
You did not physically cancel the visa. You complied with the law & reported the truth that he no longer lived in your residence. The government cancelled his visa.
This solution allows to to honor your feeling of concern that he receive the information (& ensures his speedy exit), while taking you out of the exchange (no contact!).