TS doesn't have to be offline to resize
if resize bombs query dba_extents to see which segment(s) have extents beyond the desired resize value. if necessary you can drop the rollback segments, resize datafile and recreate them w/identical storage parameters.
finally, I personally don't use datafiles > 2G. yes, Oracle has supported them for some time now but many Unix commands (compress, scp, etc.) still don't (at least on Solaris).