Impact of killing a Qnnn background process

I recently created a new UNDO TS and after insuring no transactions were left dropped the old one including contents and datafiles.

I cannot see the old file in Linux, but the space is not freed up.

Using lsof I can see that background process Qnnn is still using this file, even though is shows as /...../undotbs1.dbf (deleted)

Is there any danger to killing this Qnnn process?

Will QCMN simply spawn a new one, or should I bounce the database?

Any help is appreciated......