To be honest, from what you describe it seems like your son HAS decided on whether to keep playing and the answer is pretty much no. He's almost done with high school, sick of his team, burned out on Legion and not motivated to do the off season work required to even think about next levels — if he doesn't have the inherent love of playing that gets him past those obstacles, he may well be ready to be done. And that's okay.
In my experience, kids find (or reveal) themselves in the college search. My daughter danced for 14 years. I set up college visits at schools with dance teams where she could have danced. As we started the search process, she explained she was done with dance after high school. It took some adjustment, but she's now a senior in college and loves her life as a different person with time and energy to explore new interests.
Maybe put the time and energy into exploring his college options for next fall. Maybe put on the list schools with healthy club baseball and then he would have that option if he wants it, but he may not. It could be you have raised a great baseball fan, rather than a player??
That's a tough adjustment for parents, but my guess is, your son will be fine.