It doesn't say which side threatened to extend the strike through the end of the year. It could also just mean somebody misunderstood something; I have heard that if the strikes aren't resolved by October 1, there won't be enough time to make enough episodes of anything to salvage the winter/spring season, although I don't see why they can't extend the season into the summer if necessary.
It reminds me of the NBA strike in the 1998-99 season, where neither side looked like it was going to budge until 24 hours before the "if the strike isn't settled, the entire season is canceled" deadline, after which they "miraculously" found a way to compromise. (The only real loser in the end was WCW, but that's another story for another forum...) It looks like Congress is doing the same thing with the "get a continuing resolution passed by 9/30 or the government shuts down - okay, you can wait until 10/1, since that's a Sunday" problem.