Well for starters regarding the flow being denied due to performance or attendance. Check out 15-01

Pilots hired by Envoy after October 11, 2011 with an active Performance Advisory or Attendance Control Policy Advisory are not eligible for flow through. Such a pilot may elect to have pending grievance of an active advisory resolved under expedited procedures.

So essentially no guarantee of flow if you, at the companies determination, get sick too often.

In regards to the flow not being guaranteed, well it is only guaranteed to the extent that AA is hiring, so no protection there. I stand pretty firm however in the belief that the last thing Envoy wants to do is slow/remove the flow. They are keenly aware of how important that is to recruitment, as seen in the recent hiring numbers, that any change to that would cause a huge backlash beyond recruitment slowing.