Joel and I decided we had a couple options for fixing this issue. We could attempt to reaffix the headliner to the hull to ward off future sagging and then patch the cracks, or we could rip the whole headliner out and start over. Though I relished the thought of ripping out this particular eyesore after having it hang over me for half a decade, the contours of the surface that it covers are so domed and irregular underneath that we ultimately decided on option 1.
Joel used epoxy and shower rods to put the headliner back up in some places. Then, after trying various mixtures and combinations of epoxy, plastic welding (don't waste your time), and sealant, Joel managed to patch the headliner cracks And holes, mostly with 3M5200 caulk or epoxy. Since then, I have spent the better part of the last month of weekends priming with TotalBoat high build primer, sanding, painting with TotalBoat single part topside paint, and sanding, and painting again. 2 coats primer, 3 coats paint, sanding and wiping between each coat. It's not finished yet, but it's almost there. Take a look!