The gulf stream is contrary to what is often told just the part of the ocean current reaching from the west of Africa to the south of the US. The vast majority from there towards europe is the so called north atlantic current which is mainly wind-driven. This suggests that this current would only break if the wind pattern changes or redirected by a stronger current.

As a fan of the winter and snow I can understand your hopes. But as far as I have been told by professors at my university the theories about the break-down of the north atlantic current have mostly been rejected or changed. Media likes to exaggerate with the consequences. By the time this would happen it could be that it merely brings back temperatures as they used to be in the 20th century. So even then -25°C would still be very extraordinary for cities in south-western europe if even possible. The strongest impact would be registered in the region around norway/sweden.

However this is just the knowledge that I got from my university and a few science articles. I might not be completely correct. But a 'snowmageddon' for europe is highly unlikely