I would imagine that Tokarski would come back from Carolina. He is waiver exempt, so that gives us a combo of Tokarski/Sogaard/Merailanen that we can pass through waivers and have take the backup job by commission.
Sogaard has had a very rough year, which might have bought Forsberg time. If they trade Forsberg, I would guess it is because they have a deal to use that cap space on an upgrade somewhere else in the lineup. Trading him for the sake of trading him might not make sense without a direct replacement because backup goalies are really hard to find right now. But if trading him opens up cap to add another D, and they think they might be able to have three waiver exempt goalies handle the backup load (assuming Tokarski comes over), then maybe it makes sense.