I have never heard of Europeans assimilating in Malaysia; could you elaborate?
The Dutch language in Indonesia died shortly after independence. In fact, there is no longer a native ethnic-Dutch population in Indonesia. This is not the case simply because some native ethnic-Dutch left the region after the war and independence. It is because they mixed and assimilated so thoroughly that they simply stopped passing on their Dutch language and culture within a single generation.

Admittedly, the role played by population proportions is large. After independence, only a few tens of thousands of "full-blooded" Dutch remained in the long-term. There were already some hundreds of thousands of Indo-Dutch (i.e. "mixed"), but their assimilated identity had already been forming for centuries. Nevertheless, it is one of a few notable cases of entire European colonial populations 'going native', so to speak.

IS could have united a lot of disillusioned Libyan rebels under their wealthy banner
They could do that in Libya, even though they never even accomplished it in Syria - their backyard?

Even if Gaddafi did manage to retake all lost cities (cities which, again, he didn't have to lose in the first place), cities could still be lost again with rebels regrouping (the more Gaddafi reconquered, the more his forces would be spread thin), perhaps with support from foreign jihadists and/or islamists Or, yeah, maybe even with some sophisticated weaponry received from Gulf states. In many scenarios, the war would go on; even with zero Western military intervention.
Islamists and jihadists have and have had a relatively-negligible presence in Libya. The conflict there is far more tribal than even one such as Syria's.