Oil is big business, and if ISIS no longer controls any Iraqi oil, we can expect that it will hurt the organization's finances. However, this group is not going away just because of a little setback like this, which is why the world needs to step in and fight ISIS from every angle.
Yes, this will hurt the finances of ISIS because oil is the only way they were able to continue buying more weapons and producing their videos. Without oil, what money do they have? They will be unable to recruit new people and get their message in the ears of others.
Being able to control oil is a very big part of ISIS' plan to retain control in the Middle East. They need to have legitimate businesses bringing in enough revenue to be able to "take care of" the people under their watch. Without this source of money, I think we'll see ISIS start to lose ground.
Yes, losing control of Iraqi oil will likely hurt ISIS financially for a while until they find other sources of funding. Oil control is one big way to gain finances. However, despite what many political candidates want us to believe, ISIS is not dependent on oil as a sole source of income.