I don't believe there is any reason to question his effort or conditioning. That would be totally out of character from all we have seen over the years.
But, in my long time as a hockey fan, I have seen cases of players aging quickly. It is not the norm: most experience a gradual loss of skill. Zib might be one of those guys who has simply lost it fast.
In his defense (and I find it hard to defend his on-ice performance over these two games), he has always been a slow starter, even in his most productive years.
Once a season starts, I have little interest in how much players are making. All that matters is performance. If Zib can no longer perform as a top 1 center (or the way our lines are structured, 1A) we have a major problem.