Vivitrol is one of the least effective forms of pharmacotherapy for opioid use disorder. It does little to nothing in terms of suppressing or managing cravings. It is more a behavioral aid that simply prevents someone from easily getting high.
Does your child have any outpatient based support in terms of treatment? That will be very helpful once conjunction with the Viv if he wants to continue that treatment.
How does your child feel about the Vivitrol treatment? A lot of people are pushed into that particular treatment by doctors, family and the court system, against any genuine desire for it. When treatment is at all coercive it can easily backire, so I’d suggest having a frank conversation with your child about what they want for themselves, and then doing what you can to support their own choices in recovery. It’s their own recovery after all.
I cannot imagine many things more difficult than a parent watching their child struggle with addiction. I highly recommend you get yourself and their other parent/family your own support system. Meaning individual therapy, MBSR and peer support (the individual therapist is the most important though). The parents of children with substance use disorder need to do their own healing too.