The IS has been acting more and more like an actual state since declaring a "caliphate" earlier this year. In Raqqa, like this Vice News documentary reports, the IS is able to police, conduct Sharia court rulings, dictate how their citizens can live, dish out punishment like actual states do, and a slew of other state-like conducts. However, it is unclear if the IS will be able to govern the rest of their territory like they can in their main power base of Raqqa.
Moreover, it also unclear if the IS would be able to withstand multiple engagements from multiple offensives and still be able to maintain control over their territories. As Michael Knights notes in this latest Combatting Terrorism Center's publication, "If the ISF and Kurdish forces undertake selective offensive operations on a widening number of battlefields, the ISIL-led defense will undoubtedly become stretched, particularly if its ability to move and mass counterattacking forces is limited." A coordinated assault coming from the Kurds, the Iraqi military, US airstrikes, as well as a possible Syrian rebel element, the IS would more than likely not be able to sustain its grip on the various ground it controls. If the IS were to lose massive amounts of ground, it might persuade some groups to switch sides--especially those who have joined in either a move of collective interests or out of fear.
But, like stated above, as of right now the IS is still acting like a state. This is even more evident today with their weather forecasts.
"State of Aleppo"
"State of Baghdad"
"State of Damascus"
"State of Kirkuk"
"State of Raqqa":
"State of al-Anbar":
"State of Barka" (Hasakah Province):
"State of Salah ad-Din":
"State of Ninewa":