A few possibilities
I have no real urge to get into this again - went through the gamut with Larry J before.
But a few possible outcomes..........
1) Muslim immigrants become majority, vote in Islamic government
2) Muslims start integrating with Caucasian and vice versa
3) Muslim immigration drops due to European economic woes or immigration restrictions set up by paranoid governements
4) European birth rate starts to rise - right now is anomalously and historically low - status quo maintained.
Of these, the first is the least likely and smacks of Enoch Powell like paranoia.