I don't know about the rest of the crowd but once you rub the headliner a couple times the spray foam holding the fabric on breaks down especially after the years of heat and then the whole thing starts to sag. Mine started sagging just after the kids were old enough to reach it and shockingly just started in the back seat

. 2 other "older" vehicles I had were the same result, they were good until I tried to clean them and then started to sag.
As for removing it...I got one from the junkyard and replaced mine but in order to get it out without breaking it, the front seats also had to come out so you could angle it enough to get it out the doors as well as allthe plastic trims mentioned above.
If you were feeling really ambitous and creative once you remove the glove box you could cut part of the blower housing and make your own. After removing my housing and looking at it there was room but again your on your own for where to cut and how to get the filter to stay.