Complex sentence: Science cannot defeat death in the long run, and sometimes, as in the little girl's case, not even in the short run, but if "Love, not Death" is the ultimate reality, death will not have the final word.
Split into simpler sentences: Science cannot defeat death in the long run, and sometimes, as in the little girl's case, not even in the short run. Only if "Love, not Death" is the ultimate reality will death not have the final word.