From the OP:
I took that to mean if the Nazis fail to achieve a plurality of the votes, they will not be in power. There aren't enough parties in this scenario for the Nazis to backdoor their way into power through a coalition and Hindenburg -being little more than a shambling corpse with fascist tendencies- is not present.
If we are forced to a situation where we are voting between who is the least horrifying, surely you would want to ensure that the least horrifying fascist comes into power? Otherwise you are forced into the ethical minefield like the Catholic Church found itself it, forced to declare "a pox on both your houses" in a farcical attempt to imply there was any sort of equivalency between the Grand Coalition and the Nazis.
If the question was whether we'd rather live under the Nazis or the Fascists, I'd agree. But the OP is posed explicitly in terms of an election, and an election assumes a function democracy in which norms are at least broadly respected. The moment either candidate wins, that democracy is abolished and those norms dissolved. Who can say what happens then? Do the Fascists integrate the Nazis? Do the Nazis stage a coup? An armed revolt? Mussolini assumed power without an election, staging one after his dictatorship was legally secure; Franco didn't feel the need to meet even that flimsy respectability. Why should we assume that the political situation here is any more stable, when the only thing we know about it is that it is absolutely hopeless? A vote for Mussolini is a glass of water in the Sahara.
Besides, if this election genuinely matters, voting is a half-measure. The true patriot would simply go out into the street and start killing Nazis. If you take out at least two of them, you've already double you're own impact on the election, and it's all a bonus from there. Whatever democratic and legal norms you've violating weren't going to survive the night, and they say it is better to die on one's feet than live on one's knees.
so, democracy is defined as a "right" by the people for the people but they have no "right" to abdicate from that rule? sounds tautological to me
That's it in a nutshell. Democracy is both a right and a responsibility, and the people do not have the right to abdicate their power. Democracy, fundamentally, is not based on the people's entitlement to good government- that could come from any aristocracy or monarchy- but on the commitment of the people to govern themselves well, a covenant that the citizenry makes with itself, the terms of which to do not permit the dissolution of that covenant, or at least not by anything else that the unanimous body of the people. As long as any two people continue to uphold the democratic principle, perhaps any one individual, then the republic survives and all other authority is absolutely illegitimate.
When France fell, De Gaulle argued that the the Republic did not have the right to dissolve itself in favour of a fascist state: conservative that he was, he couched this in obscure legal technicalities which may not actually have been true, but it was accepted by much of the French and Allied public because they recognised the essential truth that a free people can no more legislate themselves into tyranny than a free man can sell himself into slavery, and that the Republic therefore falls to those prepared to uphold it. I think that something similar applies here.
