Complex sentence: He also pointed out that the document did not actually guarantee Southern Rhodesian independence in the event of a Federal break-up; when he pressed this issue, he was told that including such a clause would be tantamount to accepting the Federation's demise.
Split into simpler sentences: He also pointed out that the document did not actually guarantee Southern Rhodesian independence in the event of Federal dissolution. When he pressed this issue, he was told that including such a clause would be tantamount to accepting the Federation's demise.