Actually it went under because of extremely poor management. Fallout had nothing to do with it.
From what I remember Van Buren was nearly finished before it was cancelled in favor of Fallout Brotherhood of Steel and all competent employees were gone. Again their poor management.
Perhaps not linear in world design, but in terms of story and choices? It's extremely linear compared to the other Fallout games. Hell look at Fallout 3 MQ or Skyrim MQ vs New Vegas MQ
Edit: Others know the deal about Interplay and Black Isle far better than I do.