I assume that Garcia is either dead or has been beaten up. I certainly think he’s not in as good a shape as he was when he was kidnapped by the Trump administration.
If Garcia returns to the US, people will see he has been treated badly and may be more active in opposing Trump’s disgusting actions. I would also assume Garcia would talk about his ordeal and criticize Trump.
While I admire Van Hollen for going to El Salvador, I don’t think it will accomplish his goals.