Check the map. The town is between eastern Syria (controlled by ISIS) and Mosul(controlled by ISIS). There's no way realistic it could be held.
The main ethnic group in Sinjar (pop. 22,000) is Yazidi, who are mainly Kurdish-speaking pre-Islam Zoroastrians. The Ottomans variously slaughtered and converted them. It now looks like the end of their road at the hands of al Baghdadi.