Can my son fight being chaptered out after drug use and DUI?

If he really love's being a soldier then tell him to fight for his career and tell him I've made mistakes but I owned up to them so I've been in his shoes

Short answer; No, they do not have to give him a chance at rehab before chaptering him out.

Depending on the circumstances, involved they may choose to. Questions: How new is relatively new? Just fininished AIT or less then six years, but has a deployment under his belt. He used an illegal drug; did he get caught on a urinalysis, self report or did he have a bad reaction and request medical assistance? He got caught drinking and driving? What was his BAC? Is he under 21 in a state where any alcohol is an automatic DWI? Is there a psychological component to any of this? A recent head injury? If he has deployed how long had he been back? Any of these things MAY be reasons for his behavior.
This question is four years old so he has either been discharged or retained at this point; if he has been discharged and he had a medical issue he may be able to have his discharge upgraded. No matter what happened I hope he got the help he needed and that he is doing well.

His Command HAS to provide him a chance at Rehab. I received an Article 15 for an alcohol-related incident. I completed a therapy program and continued on with my Military career. I suggest he ask for Alcohol assessment and therapeutic support. Alcohol is capable of making very smart people make very stupid mistakes! I know! I celebrate 30 years of sobriety this November! Hope your son receives the help he needs to maintain his Military career.

It's one thing to commit these things 4, 5, 6 years into a career after going through some adversity. Those individuals have generally established some kind of career path and may need help to get back on track. There's been a large enough sample size to determine what kind of potential that soldier still has. It's another thing to do these things when you're just starting out. You're conveying to everyone that you can't be trusted with your own self-care, so we definitely can't trust you with anyone else's. I'm sure he could've been a good soldier, but he didn't prove that to anyone before making extremely irresponsible decisions. That contract he signed was his legally binding word that he basically wouldn't do exactly what he did.

My question to you is: why in the holy name if the lord would you want to keep someone (son or not) who has committed TWO serious offenses involving mind altering or mood altering substances in the Army? He is putting himself and others at risk.
You should be asking: what's the best way to reintegrate my son into civilian life while getting him the counseling he needs?
As a senior leader, I want him to transition back to civilian life and get help. Not drain Commanders and training time with repeated violations and behavior problems.

“Up until these two offenses he had been doing really well.”
lol, which indicates he wasn’t always “doing really well”
It’s easy to behave yourself in basic training.

There's probably more to the story than you know being chaptered out after one DUI and one drug-related offense there's more to it than that

Recommend your son make an appointment with the JAG to find out the real information rather then trying to ‘what if’. Okay

In my days in the Army you were given a chance at a rehabilitation treatment. Sometimes outpatient and sometimes inpatient. I did 6 weeks inpatient the draw back was one more incident would result in a chapter 13 discharge under honorable. That was in the 80's. Drugs and alcohol abuse is a choice.

Sorry, but you have got to be whacking me! If your child (yes, clearly not up to the adult version of life yet!) can't "lay off the pipe" and get serious about assuming the absolutely serious job he committed to doing, he has all but asked to face the full measure of the not so nice side of the UCMJ. If he were one of my sailors back in the day, the first arrest would be the absolute "come to Jesus" moment and any behavior that wasn't on the straight and narrow after that would have been separation time. On the wrong base, a dishonorable discharge would be standard. Your bias on what a good kid he is means less than nothing; his ability to do his job is paramount and he clearly hasn't learned one of the most important lessons in all of military service: my actions and choices impact the team and he hasn't learned to respect the team. How would you feel if he had applied for a job with a good friend of yours and you vouched for him, only to have him do something really stupid to your friends business (and possibly cost him money and clients?). Would you ask your friend to give him a second chance? He hasn't learned control OR military bearing OR respect for the team or himself.