This is great news. That said, I do think there ought to be an objective evaluation as to whether he or Zak should get the job next year. Perhaps a younger DC makes sense for a team still comparatively early in its rebuild. On the other hand, perhaps the notion that "you cannot lose your job due to injury/illness" applies as much to coaches as (most of the time) it applies to players, which might cause players to feel that denying Williams' return would violate a principle which is important to them. On the other hand, players may appreciate, if Zak gets the nod, that job security and advancement is based solely on one's contribution to the team, that performance is rewarded. I would base it on past and predicted accomplishment and contribution to the team, which would give the nod to Zak, but that will strike some as heartless, I am sure.
It's a genuinely knotty issue. Sometimes the nice thing and the right thing are very different from one another.