Oracle Database Discussions

I am deleting old data from a big table, first I deleted 2 million rows with no problems, it took 5 minutes.
I did commit with no problems.
Then I tried to delete another 8 millon rows. After 3 hours the query was still running so I killed the session.
That was a couple of hours ago and the session is still marked as killed but the rollback seems to take forever and ever.
I am the only one working against this table.

Is there any way to calculate how much time will it take to terminate the session?
Thanks