"Assyriology" is a bit of a misnomer and really means the study of cultures that used cuneiform. So it includes the Sumerians and their prehistory, which preceded the Assyrians by thousands of years. Taking it up to the Islamic conquest is stretching it a bit, but I suppose there was a lot of continuity between that period and the thousands of years of cuneiform use in the region. E.g. the latest cuneiform tablet known is from 79AD from the city of Uruk, which was inhabited from about 5000BC to 700AD