I don't think Wizz would leave LTN either as much as anything because a fair chunk of their network is replicated at STN by FR and I can't see them getting the slots they would need at LGW. But, what I think is plausible is that they move a few services over to one of those airports (most likely STN) as a warning shot/bargaining tool. Routes such as Debrecen, Belgrade and Bourgas where there is no competition, and Chisinau, Split and Ljubljana where they would be less afraid of the competition.