just spoke to customer services at balkan holidays asking about the lack of snow in borovets and they said that they do not offer any transport to different resorts even if there is any snow at the other resorts-that is up to the individual.
also said it was still too early to think that there won't be snow for xmas-just hope she was right
Tour Operators are under no obligation to tansfer you to another resort. Check your insurance, some will refund your travel expenses to another resort.