JHE said:
1. Mozzy birth rates do not massively out-pace indigenous European birth rates?
2. Mozzy immigration is going to stop or greatly reduce?
3. Mozzy commitment to Islam is going to reduce?
Answers to these depend on the time-frame you have in mind.
1. This is certainly true for Pakistani and Bangladeshi people in the UK. Contrasts in the lifetime fertility rates for different ethnic groups are particularly marked in London. You can find these by hunting around on the Greater London Authority's website.
ViolentPanda makes a good general point about birth rates for ethnic groups falling into line with that of the 'host' population. This has happened with the Black Caribbean, Indian and Chinese birth rates. But a similar decline to convergence in Pakistani and Bangladeshi birthrates is thought unlikely to occur before at least mid-century because of (a) lower levels of female economic activity in those groups and (b) arranged marriages involving spouses brought in from countries where high birth rates are the norm.
2. Sooner or later some governing party, probably the Conservatives, will act to reduce immigration, as is already happening elsewhere in Western Europe. There will doubtless be attempts to claim that 'it's not about race', but of course it will work out that way. Unlikely, either, to be quite as pragmatic as the Dutch 'gay men kissing on a beach' video shown to prospective immigrants to Holland (pretty obvious who that's meant to put off).
3. Very hard to predict how that will work out. 40+ years ago, for instance, when France and Britain imported (or lured) large numbers of workers and their families from predominantly Muslim countries, Islamism wasn't on the radar. 40 years hence, things may be very different yet again.
(Referring back to point 2, there is a section of the establishment whose developing ideas on ethnic conflict and, possibly, immigration is overlooked, and that involves senior military staff, and military and intelligence planners.)