The impact of Brexit on Wizz will be most interesting to observe. We know that EU nationals living here already will have the right to continue to do so, and there's no obvious reason why Brexit will have any substantial effect on their marginal propensity to fly. So I wonder whether we will merely see a plateau in the growth of Wizz's UK ops, rather than a more notable diminution.
We don't know for certain whether or not those here will be allowed to stay as our illustrious leader can't or won't give them that assurance, but like you, I believe the reality is that they will. There may well over time be a "Canada" effect, where relatives die, and the urge to "go home to see the folks" diminishes.
Personally, I think that migrant workers will continue to come to the area to do the jobs they do now, in similar numbers, as in the real world British people simply don't want to do the work on offer, and would rather sit on their backsides whinging that they can't get jobs than take those that are available.
If the government were to really tighten up on migrant workers, and force those "can't work / won't work" in the population to work, then Wizz could suffer, as they may from increased automation in agriculture and horticulture