If Samaras can't get enough votes for a president in parliament, which he won't, then there will be snap elections. Even with polls saying Golden Dawn is down to 4%, unbiased polls by newspapers like Acropolis say it's really at 18%.
The way polls in Greece work is newspaper analysts call your house and ask you what party you support. Obviously, most people are paranoid about being murdered, fired, or imprisoned, so people that support Golden Dawn often give the answer "undecided".
When it comes time to cast ballots, however, the real numbers come to light. Last European election Golden Dawn got almost 10% of the national vote (making the third largest party in the country), despite polls projecting they'd get 5-6%. Additionally, Kasidiaris got 16% of the vote for mayor of Athens, which put him close to the 2 mainstream candidates, even though Kasidiaris was campaigning from jail
Once we get to see what the Greek government has up its sleeve during the upcoming trial of Golden Dawn, Samaras will lose all of his credibility.