One thing that can happen is for the Alliance to form a minority government and get votes from the Swedish Democrats for a budget and so on.

Just about the best scenario for the Swed-Dems as they can claim credit for whatever good happens and always fall back on, "WE weren't in the government!"  

From an outsider's perspective, the Liberal and Center party leaders would have to be out of their minds to go this route.  They would get beaten-up for whatever bad things happened AND they would be seen as allying with the Swed-Dems, simultaneously pushing both their Right and Left wings away from the party.

She believed in nothing; only her skepticism kept her from being an atheist. -- Jean-Paul Sartre