I think it depends on what time of the year we are talking. If It's by mid-season summer, then I think McDermott (or one of the other AAA pitching prospects) gets a call. If it's before then, I think Teheran is the #6 starting option at least until Means returns to the rotation. Although, that could very well just as easily be Suarez as much as Teheran. But I think Suarez might be looked at more for the bullpen.
Until June when some of the prospects might be ready at the earliest (and prior to expecting Bradish to return), I see the starting the starting rotation pecking order to look something like this...
1.Burnes
2.Means (IL, expected to return in April)
3. Rodriguez
4. Kremer
5. Wells
6. Irvin
7. Teheran
8. Squarez
9. Zimmerman
Then when we get to June, I think McDermott jumps up above Teheran unless Teheran has been showing himself to have success. Of the minor league starting prospects, I see something along these lines...
1.McDermott
2.Povich
3.Johnson
4. Armbruester
5.Stallings