SQL won't automatically KILL running tasks.
Your best bet is to force them to recompile immediately. AFAIK, the only way to do that is to have it affect the entire db using the FLUSHPROCINDB command:
DECLARE @db_id int
SELECT @db_id = database_id
FROM sys.databases
WHERE name = 'your_db_name'
DBCC FLUSHPROCINDB ( @db_id )
SQL DBA,SQL Server MVP(07, 08, 09) A socialist is someone who will give you the shirt off *someone else's* back.