Justin Harrell lasted at least four years and so did Perry, but both were early busts due to injury. One worked out while the other didn't. Sherrod also lasted into his fourth season, but again had fought a gruesome leg injury for years.
Datone Jones was I would say the only non-injury disappointment player. He also lasted four years but I think that the staff still saw potential in him, and tried to change him into an OLB.
So the statistics seem to indicate that a first round pick generally gets to play out their 4yr rookie contract, unless they are a spoiled brat that quits on his team. If he hasn't been berated yet, Randall needs it now with the clearest and strongest message that you're about to get fired.