Legally you are still responsible for him and most of his actions. If you do not report him as a runaway (even if you know exactly where he is) and he breaks the law before turning 18 it doesn't look very good in court. Say he does something minor like vandalized property ( I use the term minor as in comparison to a big felony like auto theft) the court will still look to you for payment of damages, fines, etc if there is no record of you reporting him as a run away. Cover your butt legally and file the report.
yes, is he truant from school, yeah, at least let the law know what has happen and your child, who will always be yours needs to be at home where he can finish growing up. adults get to leave home not kids..
If he manages to not come to the attention of the law for the next two months, you're fine. DO NOT report him as a runaway, they won't just return him to you, they'll lock him up. Juvie judges are answerable only to god, he will have no right of representation, and juvenile detention facilities can be pretty terrible. Remember that Nature thinks he is an adult. Let Nature takes its course.