Having a muslim mayor does not equate to genocide. In the most reliable brexit maps London voted to remain, so of course the mayor is going to have similar views with the people in the city
A "few generations" could mean anywhere between 2050-2100, I doubt Europe is going to look like Saudi Arabia by then....or ever for that matter. I don't think a bunch of mussies is going to get rid of European culture, if they didn't in ancient times they won't do it today. So no, there is no conspiracy for the mudslimes to take over Europe.
Would you say there is a Japanese genocide? That country has been having problems with birth rates for a few years now and its actually to the point to where the country is declining in population.
What I would really like to see is for Britain and other European countries to have votes on the immigration polices, the will of the people I always say. If one country wants to keep the migrants flowing let them, if another wants to ban migrants (no matter the religion) then they should be allowed to do that to.