With the result not yet decided, let alone the negotiations that will almost certainly follow, it seems to early to go for the "at any cost" line. Labour may well hold a tough line with the SNP and avoid making some sort of dodgy "throw everything at Scotland" deal. And, equally, who's to say that Cameron won't find some coalition to prop himself in power at the expense of being dragged way over to the right?
Not to say that the latter is more likely, somehow, but it seems a bad idea to fight an election campaign based mainly on second-guessing what follows hypothetical negotiations. Shouldn't the Tories be working on selling their record in the last five years? All this negative politics is very frustrating.