This too shall pass.
The exact same thing happened to my son who was kicked out of his rehab and driven to the nearest city. There was no vacant bed or even blanket available at the shelter so he slept in the parking lot. This was the very thing that changed the course of his recovery.
He had been there for three months bucking the rules. After the shelter incident he called and asked to come back to the rehab. and has been there now for a total of almost 10 months.
My son did call me collect from the city he was dropped off in. I told him I hoped he would the the right thing at this crossroad. He had a choice the streets or plead to go back to the rehab that I am paying for. Luckily, my son chose the rehab and they took him back.
hang in there mom...your son most likely will choose to go back...and be serious about his recovery after having seen the alternative up close.