I'll be honest, I've never heard of this particular hassidut (wikipedia page here), but at least this "prophecy" will be easily checked. I've long had a policy of not taking my stock advice based on random postings on forums, or based on anyone's Ruach Hakodesh - though I'll admit that so far this policy has not generated any great revenue for me. In keeping with my policy, I'm willing to confide that I've yet to change my stock holdings, but I am interested in seeing how this will play out. If the stock market really does do a major nosedive tomorrow, I will repent my lack of faith by posting a picture of myself eating a hat on Thursday (not black - I don't own a black hat). Comments on the Rotter forum, seem to suggest that there are not enough Premishlaner Hassidim to make this prophecy a self fulfilling one.
I was intrigued to discover who the Premishlaner rebbe was - and have found this video of him - playing a violin no less. The tune he is playing does sound rather tragic.
I've also managed to find this video - A tish during Hanukah: