Rollback segment can grow as any data segment provided Maxextents is not reached and Diskspace is available.
i.e. it can grow to a size of 166500 datafiles for a TBLSP * 34G ( on 64bit solaris ) = 5661000GB, or less than maxextents for ur Rollbacksegment ( I dont remember maxextents for Solaris ).

Thanx
Sanjay