That makes no sense at all. Democracy doesn't work like that. Only the people of Scotland have the right to vote on Scottish secession, in the same way that only the people of the UK should have the right to vote on whether to leave the EU. If a member is considering leaving a club that is a decision only that member can make. If a non-member is applying to join then that would be a different matter and a question on which all existing members would expect to vote. In free society you ask to enter but you are free to leave, otherwise you are enslaved.
If "yes" voters think that the only reason not to hold a UK wide vote is that they might not win it then they do not understand the most fundamental principles of a free society, which is not an auspicious start. And I think they may be wrong. I suspect a UK wide vote might increase the yes vote. I for one fervently hope for a yes. I just think its a tragedy that Scotland has chosen such abysmal leaders with neither the intellect nor the statesmanship to preside over the successful and harmonious establishment of a new country so that whatever the outcome this issue will not be fully resolved and the injury it has done to relations between Scotland and England will linger like a bad smell to trouble future generations.