How to recover a carboy of cider? I'm one of those people who puts nearly all my energy into things other than brewing.  And yet I still do it a little.  That's why I have a carboy of cider that is 18 months old in my basement.

I don't know if the cider will be good or not when I try to bottle it, but I do know that all bubbling stopped long, long ago.  I'm not sure if all the yeast is dead at this point (does that happen?) or if all the sugar is gone.  Seems like one or the other must be true though.

So on the off chance that I don't need to just pour this down the drain, what's my best bet for getting it carbonated in the growlers?  Yeast?  Sugar (though I actually used all honey initially)?  Both?
First, I would check to see if it's still drinkable. You might have a carboy of apple cider vinegar if you haven't put any sulfites into it or somehow prevented from oxidation. The way to test it is to get a siphon (that you have sanitized) and suck out a little to taste. If it tastes ok, then you need to prepare for bottling. 

I would follow these directions except when it says to prime with 1/2 cup of corn sugar, I would put in a little yeast (maybe a tablespoon?) and mix with some water before you bottle. Make sure the yeast has dissolved. I'm sure the yeast in your carboy is dead at this point.