Three core players (Tyler Myers, Drew Stafford, Ville Leino) underachieved in 2012-13. The best data for predicting their production this year is past production; I looked at 4 regular season stats (games, shifts/game, points, +/-) for these players for the past 4 years (2009-10 to the most recent season).
Tyler Myers has played nearly full seasons the past 4 years, and has been a consistent 28 shift/game player. His points/plus-minus stats starting with the 2009-10 season are: 48/+13, 37/0, 23/+5, 8/-8.
Drew Stafford has also played nearly full seasons, and has been a consistent 21 shift/game player over those 4 years. His stats, starting with the 2009-10 season, are as follows: 34/+4, 53/+13, 50/+5, 18/-16.
Ville Leino has likewise played nearly full seasons (for Detroit and Philly in 2009-10), except for the past year when he was limited to 8 games. He has been a consistent 18 shift/game player across the past 4 years. His points/plus-minus stats are: 11/-8 (combined Detroit & Philly production), 53/+14, 25/-2, 6/0.
What predictions can we make from these data? Of the 3 underachievers, Stafford's past year represents a clear departure from the consistent 2-way game he played from 2009-10 to 2011-12. The data suggest he could rebound with a 50 point year if he gets consistent 2nd line shifts. Myers' past year, by contrast, reflects the clear downward trend in the previous 3 years. Clearly the Sabres are concerned with Myers' declining production: this is evident in the Tallinder and Sulzer moves, and also in the recent draft picks. Leino's past production is so inconsistent and confounded with injury that predicting his future performance is unwarranted.