Decreolization is a postulated phenomenon whereby over time a creole language reconverges with the lexifier from which it originally derived.
As languages remain in contact over time, they typically influence one another, especially if one holds higher linguistic prestige.
[1] According to Peter Trudgill, if one views pidginization as a process of simplification, reduction, and admixture from substrate languages, and creolization as the expansion of the language to combat reduction, then one can view decreolization as an 'attack' on both simplification and admixture.
... What historical linguists outside of creolistics study is language change, be it contact-induced or not, and language change is a process that is presumably based on universal psycholinguistic mechanisms that do not leave room for a sui generis process of (de)creolization.
[3] Furthermore, it has been shown that linguistic changes resulting from contact between a creole and its lexifier do not always emerge in the way decreolization would predict.