It has always been the case where Senator Conroy has desired this filter, he has long been a pawn of the Australian Christian Lobby.
Before the recent elections the party he belongs to, Labor (a middle left party), could have passed it on their numbers alone, however the recent election puts Labor into a minority government position.
Even with the Labor parties internal rules saying that all members must vote to the party line they are simply outnumbered, everyone else in government is on record as being against the plan.
Now there is nothing to say that Labor can't strike a deal with the opposition party and the independents who make up the majority of the government, say tie it being passed to not putting a price on carbon, but I think the chances of that are slim. A minority government is a very tenuous hold on power.
As far as a conscience vote, all other parties are free to vote how they like, members of the Labor party are the only ones tied to the official party line, however for things like Gay Adoption (recently passed) and Abortion (passed quite a few years ago) those rules are relaxed.