There is really no easy answer to your situation because if you had to follow the letter of the law, it would be far too cumbersome and costly to get rid of this roommate.
However, it appears to you've taken all the necessary precautions to protect yourself from any wrongful eviction claim. I agree with your assessment that with all of the factors you mentioned, he's abandoned the room.
The information presented here is general in nature and is not intended, nor should be construed, as legal advice. This posting does not create any attorney-client relationship with the author (who is only admitted to practice law in the State of California). For specific advice about your particular situation, consult your own attorney.
Disclaimer: The materials provided below are informational and should not be relied upon as legal advice.
If you signed a lease with this person, and he is delinquent on payement of rent, you will need to give a proper 3-Day Notice. If he does not cure default within the 3 days, you will bring an unlawful detainer action for a court order to evict the person, declare forfeiture of the lease, etc. If this person has issued checks to you on a closed bank account, you can give them written notice based on Section 1719 of the California Civil Code, and if he fails to cure, you can sue for the amount of the check, plus treble damages (limitd to not more than $1,500). You should consult your own attorney to protect your legal rights.