What happens when you kill a rollback session at OS level?

Hi,

We have a process with a huge update on a very large table (500 Gig). We had to kill this session in our RAC environment after millions of rows are updated (not committed). What happens if I kill this rollback session at OS level? Will the rollback be completed in the background? Will the table be accessible after killing the process at OS level? Any input is appreciated. Our rollback process is still running and we might let it run in the worst case.

Thanks