They are not ruling it out, but there's really no reason to rush him or stop him from starting just yet. Just enjoy the euphoria of what he did yesterday. He could still turn out to be Mike Grace or Tyler Green (or Marty Bystrom) more than Curt Simmons. He could also end up starting again. Or being traded.
I quite like Dombrowski's comments on Alvarado. Yeah, it's a big loss. But it's just like having an injury. You get through it. If you can live with Kody Clemens as your 1B and Edmundo Sosa as your SS for several hundred innings when Bryce Harper or Trea Turner gets hurt, you can fill some relief innings for the next two months, even if it won't always be pretty.
And the plus side, if I'm not mistaken, is they will able to bank his lost salary in the CBT calculations, which may give them a little more to play with at the deadline.