How to handle swollen MacBook battery after several weeks of storage?
Can I expect that the danger of fire is lower after safely storing it
  for this period of time and not observing any changes?


No. It may already be deeply discharged, or it may be 50% full. No way to tell from "the state of charge was unknown" and "it has been a while".


  Do you think that there is still danger in unscrewing and removing the
  battery?


No. A battery is not nitroglycerin. Moving it without bending or pressing on it is safe. I'd say that it probably can be removed from the device without significant mechanical stress, so the 'risk' depends on how careful you are. You already know that you don't want to apply force to the battery in the process, but I believe you won't have to.

I feel that the risk of letting it sit where it is is much higher than removing and securing it a.s.a.p. If it starts to burn right now, at least the MacBook will burn too, so get rid of the battery as soon as you can.