litefoot, so a hail mary situation or two?...........
been there myself a time or two.......or three or............
like perry, and unlike being taught 'take your losses in the fall', i have 'nursed' and done all sorts of 'hail mary' things to salvage a hive. and for me mostly from my mistakes, or lack of attention/judgment. in the fall this is more difficult when hives are in trouble. sometimes trying to save a hive flys, sometimes it doesn't. we learn from our mistakes. i have just taken and learned another hard lesson this fall. still reeling and thinking over a loss of a very strong hive.
no brood at this time of year is normal. if you have no queen in #1, these bees will not make it, irregardless of how much you feed them.
did you miss finding her? queenless bees will die off, or possibly abscond.
hive #2~ do you have a queen?
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The other colony, which was nursed through the summer after a laying worker incident, is a deep and medium with no resources (food-wise) to spare. It's too cold to continue feeding 2:1. I can try fondant, but I don't think they'd survive the whole winter on that."
if you already think this about this hive not being able to survive with fondant added? most likely true.......one never knows until one trys even with odds against......it's how we learn. i would be inclined to combine it with the other hive based on what you said. if you combine them and whatever resources, i would add feed and i would not let the feed run out.
about combining, not sure if your temperatures are conducive for combining hives?
maybe kick out the empty deep on hive #1, if it's too cold to do so, just leave it. set the boxes from hive #2 on hive #1(newspaper between) and again feed fondant or whatever on top. if you have two queens, let the bees figure it out.