Hi, Lady!
I've never seen any research linking depression with brain degeneration. I was diagnosed 15 years ago with major depression recurrent. I've had my ups and downs but only 3 MAJOR depressions in that time (currently trying to come out of one now). I haven't noticed any degeneration; in fact, during my last major episode like 8 years ago, I went to grad school.
Now what I HAVE seen research on and keep hearing on the news lately is that it has been discovered that multi-tasking is not good for a person - it actually makes them less efficient. You mentioned you like multi-tasking (and I've worked with others who do as well), but that's something I really think takes a toll on the body and brain.
I agree with faye that you can recover the type of job you enjoy doing.