what data is missing?
all data from a table?
some data form one table?
some data from multiple tables?
Data can rapidly be removed with a TRUNCATE statement. (think of opening a file as output). Nothing is logged. but that removes all data from a table. without logging the data.
RBS cannot be extended? So something is running that used up all available roll back segments? Is it possible that this job that used all the RBS is holding locks on the missing data?
I think your first task is to find a DB person. they need to address the RBS situation, then determine what happened to the data.
At worst, there is always recovery. followed by a review of your security. because, maybe, someone did remove your data.