Lines - there are a few ways to teather dogs to sled. If you are in the most northern wide open expanses, where there are no trees, and you are using dogs to haul supplies, expedition style, then the native way would be to tie each dog individually by the back of the harness to the sled, forming what's called a fan hitch. It allows all the dogs to choose their own path. This only works in barren hard country, or over ice fields, where a standard hitch would cause the dogs trouble.
What you see in the photo is a standard hitch. One gangline runs through the team, the dogs are in pairs and each dog has a line (which he pulls) called a tug line, which is longer than the dogs neckline (which he doesn't pull) which simply keeps him moving forward, in the same direction of the others. The width of the two dogs is the width of the sled, which is key on trails through the woods. This is what you see in that pic. Look closer and you'll see each dog is connect to the mainline by 2 lines.
Food - I can't really say how much because I don't know their strategy, how they resupply, etc. If the dogs are sleeping on a picket line, without a house, they'll go through a lot more food and they will need higher fat content. In the extreme north it's common to feed salmon, moose, seal, carabou, etc. and then snack with fat treats based on caloric needs.
Retirement - this is obviously something that is pretty touchy. Dogs come and go but 'the team' remains... and the strength of the team is limited by the weakest dogs and at some point they need to move on. In racing, races are won by leaving dogs at home that cant make it. culling happens very early, and the dogs that make it to racing retirement age can still run on a touring or recreational team until they die on the chain at a ripe old age. It's not uncommon to see 10 and 11 year old still working. As far as turning them into pets, it depends on the dog. With some patience and understanding, an old dog can become a couch dog. But a 3 year old will usually just destroy your house.
I always had great dogs which were in demand and didn't keep any beyond 7, so depending on the dog, I'd try to find them a place they could be happy and fit in. On occasion, in the case of sick or dangerous dogs sometimes this wasn't possible. To be honest, it's the ruthless culling of young dogs over countless generations who don't work out that made sled dogs the genetic marvels that they are today. But that is another issue. I think the issue they have is that they probably have no one that wants them. Remember, where there is one sled dog, there is more than one. Where I lived in Alaska, there were 600-900 in a half mile radius of my cabin, depending on the time of the year.
