I hesitated in responding as I am pretty direct and usually accused of not being sympathetic or understanding.
Realistically, the chances of playing beyond this point are probably not good.
Understand that independent ball is made up of former pro players trying to get back into the game or looking for playing time due to recovery from a prior injury and from what I understand they are not always well scouted. Does your son know of a scout that he could talk to about this? Most players I know going into independent ball get in because of a relationship with an agent or scout who recommends them.
He might want to contact teams to see if they have MLB try outs in the area.
He doesn't have to be done with the game, there are so many ways that he can get into it on a different level. I don't know what his major was, but there are so many jobs in baseball that do not always include playing.
I wish that every young man could play the game at the pro level, it would definetly open the door as to what exactly it is all about, it is not what you see on TV, and for a free agent, it is extremely difficult to try to find your way into the line up.
BTW, you used the word WE, so is this something he wants to pursue or something that you want him to do?
Best of luck!
TPM is correct, It's better to walk away from baseball due to injury than to be unwanted after 17 years of playing.