Complex sentence: Australia's participation in the 2015 contest was set to be a one-off event, the plan being only to perform again the following year had they won, but it was confirmed in November 2015 by SVT that they would participate in the 2016 contest.
Split into simpler sentences: Australia's participation in the 2015 contest was set to be a one-off event, the plan being only to perform again the following year had they won the contest. It was confirmed in November 2015 by SVT that Australia would participate in the 2016 contest.