hello, very sorry about your situation, i hope all goes well but
in reply to your worries about your other dog not being able to cope with the loss ..i have had a similar experience, two of my dogs one being a GSD also a rescue from deathrow lol, the other a pointer x cattle, they were bestfriends and one day the GSD was bitten by a snake whilst noone was at home he died from the bite, our pointer was devestated he didnt move out of a little corner in the backyard for a few days, he wouldnt eat, he just cryed, we brought him into the house but still he didnt move from the one spot, This was very strange considering how much he usually craved attention, he was never really the same until we got a new GSD quite a few months down the track and he adores her, he is back to his old self again, Although i dont doubt the fact that he still misses his old friend, he is a very happy dog again. Full of life and as happy as larry.