Well, Spiderpig was doing really well the week after we took him to the vet. He was eating quite a bit, his poops were fully formed and solid, though we still had to clear his butt about twice a day. We continued expressing his bladder, doing it more frequently and noticed it seemed to help with a lot of the discoloration and sediment.
Sunday I noticed that he was beginning to behave "oddly". He was still moving around a lot, still eating, but I noticed he would "trip" and lie on his hind legs every so often for a moment before getting back up. He also felt a less "solid" when I picked him up, if that makes sense. I didn't think too much of it because it seemed like he was otherwise doing fine.
Monday morning my wife tells me that she doesn't think Spiderpig is going to make it and when she took him out to clear his impaction he was barely responsive. He wouldn't eat the lettuce or carrot given to him and just lay completely on his side. His mouth was hanging open and aside from the occasional yawn, didn't exhibit any movement. She placed him on a 2x2 fleece, wrapped him lightly, and placed him in one corner of the cage with the vegetables.
I woke up about an hour later to get ready for work and checked in on them. His roommate, Piggle Rick, was in the opposite corner, not touching his lettuce or carrot, either. Which was strange and I guess he knew what was to come. Spiderpig was in the shape that my wife described him; his breathing was barely perceptible at this point. The visual reminded me of Magneto when he was on his very last legs.
I pet him for a bit and he was still warm, but unresponsive. Spent about 10 minutes with my hand on him before continuing to get ready for work. I dropped my son off to daycare and came back. By then I was pretty sure he had passed because I couldn't notice his breath, his body started feeling a bit cool to the touch, and his eyes got really milky. I wrapped him back in the fleece, put him in a carrier, and my girlfriend brought him to his vet later for cremation.
Piggle Rick had a day where he didn't seem to be eating much or moving much. But today he seems to be doing much better and is eating normally, pooping, etc. We're going to find him a new roommate soon.
It's weird that he suddenly turned for the worse overnight, but overall I'm happy with the time had with him. We had him since he was a month old, and it's been a solid five and a half years of joy that he shared with us and the 4 roommates he's had over his life.