The SNP stands no chance of winning the Scottish Elections outright, nor is there any chance of a Yes vote in a referendum on independence, so Gordon Brown can sleep easy. Furthermore, there is no doubt whatever that an Act of the sovereign Parliament of the United Kingdom prevails over that of the devolved Scottish Parliament, which itself exists only pursuant to an Act of the former kind.
That the sovereign Parliament currently chooses not to enact legislation applicable only in Scotland, or that Ministers drawn from and accountable to that Parliament currently choose not to exercise their statutory powers in Scotland, is neither here nor there. It may do so at any time, and they may do so at any time. Under Brown, they and it would probably have done so anyway, as would also be the case if there were to be a Conservative majority in the House of Commons. If a Brown Premiership faced a non-Labour Scottish Executive, then this becomes an absolute certainty.
If people voted SNP in ever-larger numbers in protest, then that would only harden Labour and Tory Unionism. Alternatively, ever-more Scots might find themselves wondering what their never-popular devolved Parliament was for, and begin to hasten its demise by the same authority that created it, namely that of the Parliament of the United Kingdom.