Complex sentence: Around 70 people died during the street fighting and between 700-750 persons were abducted, who never retunred, by Sayyaf's Ittihad and were most likely killed or died in captivity.
Split into simpler sentences: Around 70 people died during the street fighting and between 700 and 750 persons were abducted by Sayyaf's Ittihad. The kidnapping victims never returned and were most likely killed or died in captivity.