Also known as the global strategy of how to handle North Korea.
North Korea is resource poor, bankrupt, and starving - it took decades to build up nuclear capabilities, but they did it.
ISIL has oil, and lots of it. Sure, you could make selling their oil 'illegal' like blood diamonds, but the strategy didn't stop DeBeers from trading blood diamonds, and it won't stop the oil companies.
ISIL may not be able to obtain nukes, but they are well funded enough to do other terrible things to nations who would just as soon ignore them.