It's a mutual option on Bader, those almost never get exercised.
He's a high-end defender, though he's mostly been playing LF this year. If he plays CF and Marsh goes back to LF that's probably worth 1 WAR the rest of the year.
I don't think there is any reason to expect him to regress in August and September. Sometimes guys actually make adjustments or had health issues [which he very much did in '22 and '23]. It's no crazier to think that he'll be good for two more months as it is to think Bohm or Stott can get back to their best selves.