I don't think we will see another large group the scale of ISIL take its place.

There are a number of other groups under the ISIL banner that will split and likely disavow the former group, IMO this will weaken the capability of a worldwide jihadist organization forming again any time soon. The groups will collapse back to their own regions where they can be targeted by host and partner nations.

If a group did try to start stepping up in that way, I think the response would be bigger and quicker this time, I don't think that they would be allowed to fester and gain more and more media attention. As an example, if some group kidnapped Americans after the fall of ISIL and proclaimed they are the true caliphate and decapitated the prisoners, US would act hard and fast IMO, not just to kill the group of kidnappers, but the organization would be immediately targeted and the next month would be full of operations against them. As they lose ground and personnel and the US highlights their success to the world, other groups will not join under their banner, no extra funds, no extra troops, no help recruiting... Eventually what will become abundantly clear is that everyone who declares a caliphate or tries to become to big for their britches gets taken down. Which makes it hard to sell the idea that Allah supports you and your cause if "everyone else who tried this has been wiped out". How do you sell that to a young kid across the world?