HH....I know its hard not to worry. I am not in the exact same situation as you but I have two kids not living at home and the one idiot living here. With the one who is living here and causing me the problems what I have trained myself to do is simply refuse to worry about him if he isnt here. Most of the time I am dead on right when he fails to show up...he has been picked up or is in trouble. If I worried myself sick over it I would get nowhere...he has to deal with his messes.
Now I also have my middle son who is actually in a semi dangerous profession and moving into a more dangerous one. He has trained me well to deal with "no news is good news." He will become a cop up in Maryland sometime in the next couple of months after he gets out of the Marines. I simply cannot sit home and worry about everything he is doing or I would go nuts. I used to worry every day that I would get the knock on the door telling me he was killed in the Corps. Well he made it thru. Now I just live with no news is good news. If something happens someone will find me.
Same thing for you. If something happens to your son, someone will find you...they will. As long as you dont hear anything, you can rest assured he is just fine.