Oracle Database Discussions

I've got a quick question:

I'm using 11GR2 on Linux RHel 5.

Question is that if there is a very large rollback operation going on that is lasting too long for comfort and our management says to kill the rollback transaction because it is holding a lock on the table, what would be the result?

So far, we've killed the transaction at the OS level, and the table lock is freed. How can this be since the transaction still has to roll back or we would have inconsistent data?

Is this something smon restores in the background process using UNDO space to hold any new transactions to the table while it is being rolled back?