The fact is that if you compare the actual sets of numbers, the truth reveals a very different story.
The following is a short summary of the last six General Elections in the UK. For 1987, I've included the SDP–Liberal Alliance as the Liberal-Democrats, because in 1988, that merger was formalised anyway.
|650 Maj 325||1987||1992||1997||2001||2005||2010|
|591 Maj 296||1987||1992||1997||2001||2005||2010|
For all of these elections, there were 650 members and a majority of 325 required on the floor for government (owning to the peculiarity that one member would become speaker). This is irrelevant anyway as in every general election, this doesn't matter.
If we pretend that Scotland's 59 members never existed, then the slightly smaller House of Commons would only have 591 members and require a majority of 296 to form government.
What's telling is that of the last six General Elections, the only difference is that the Conservative Party would have formed government in its own right in 2010; rather than needing to form a coalition government with the Liberal-Democrats.
Actually, if you extend this all the way back to the time of Churchill, then only with the hung parliament of 1974 in which Harold Wilson formed government and ten years previous in 1964, would the lack of Scottish MPs have made a difference at all. On those occasions, instead of Labour governments, there would have been Conservative governments formed with very small majorities.
In 1987 the Thatcher government held a very strong majority; whilst in 1992 John Major's government was elected with the single largest number of raw votes in British electoral history. Tony Blair's 1997 win produced a massive change in the number of seats as did the Cameron government of 2010.
What's not stated in this whole discussion is that it isn't Scotland which has the single greatest sway on the results of elections but the 79 seats of London.
I think that the premise that the UK would be condemned to perpetual Tory rule if Scotland leaves is flawed on the basis that the numbers simply don't work. What might be unclear is what would happen in the 2015 election if the Lib-Dems again end up as kingmakers caught between the Labour Party and the Conservatives. Considering that they were actively fought against when it came to the issues of tuition fees and the Alternative Vote, would they be so willing to try that again?
The House of Commons will basically continue to operate as it always has done. If Scotland leaves, although they take 59 seats out, it is still the public barometer which determines who is returned to government and it would appear that without Scotland, not a whole heap actually changes at all.