You won't be able to take the database offline with a session still rolling back. Restart the SQL instance, that will remove that SPID, then you'll have no trouble taking the DB offline to move it.
DO NOT try to kill OS threads, you could crash SQL.
http://sqlblog.com/blogs/linchi_shea/archive/2010/02/04/killing-a-sql-server-thread-don-t.aspx
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