Is he better than Witherspoon? I think Dunbar is definitely better than WW against the run but maybe not against the pass. Witherspoons contract is guaranteed so they wont cut Wil. But Dunbar of last year is an upgrade over the slower Spoon.
So, do they bring back Dunbar and bump Bates or Armstrong? The push to be a young team would make it seem unlikely.
If they did bump one of them it would be Bates. However they could cut someone from another position, like RB since they have a plethora (as El Guapo would say). So, is Dunbar more valuable to the team than Chance Reynolds? I would think so. His aggression and enthusiasm is good for the team.
Then the real question is 'Can he still play with that level of aggression and enthusiasm without the substance that he tested positive for?' (maybe Cocaine? as rumored). I doubt it, but the coaches know what they saw on the practice field. If they think he still has it in him then they bring him back.