Worst case is TJ surgery and his progress is set back a year.
But with De Los Santos and some other pitchers emerging, waiting an extra year wouldn't be the end of the world.
And like SD, it may turn out that Sixto's future is as a closer, not a SP.
Given we have five starters, and the Lehigh rotation by August could be De Los Santos, Kilome, Irvin, Romero and Anderson (not to mention Lively, Eshelman, et al), there was no need to rush the A ball pitchers in any case.
Sixto just has to time it to arrive in 2021 to replace Arrieta!