The phrasing of the poll (Golden Dawn having the most seats) is something that certainly could happen if New Democracy and Syriza both implode, which is perfectly possible. However, and this is key, there are no parties which will form a coalition with Golden Dawn. The only way Golden Dawn can democratically gain power is by an absolute majority in the Hellenic Parliament, which it does not have the electoral strength to attain, period.
As for non-democratically? Only if alien space bats help them out.
I think at this point it is wiser to say that it is
highly unlikely, than that it could n
ever happen.
The situation is more desperate for many people than we care to acknowledge and if it gets worse anything can potentially happen. About half the police are Golden Dawn supporters and they
do have a certain amount of support in the army. Noone really knows how the most right wing part of the Greek army and upper class would react to a Socialist development. If they can't decide what to do, you
can construct a scenario in which Golden Dawn gets into power simply by being the
most determined and well organized group in a chaotic situation. A military coup is still more likely in this extreme scenario, so we are talking about a very small risk, but you don't need alien space bats to do it.