Kill the query so that the user gets annoyed and re-runs it?
If you're running out of space for TempDB you need to either change the queries so that they use less TempDB or you need to give TempDB more space.
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