In my experience, the 0% complete, 0 seconds remaining rollbacks tend to sit around forever. It would be waiting for an external resource, so do check, but those ones alone are usually safe to restart SQL to fix (only the 0% complete, 0 seconds rollbacks)
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability