As someone who's had Ulcerative Colitis for 6 years, this is a completely life changing disease.
When you're not in remission you're pretty much a corpse. Can't imagine how he was able to fight while flaring up. Must have been a mild flare, but regardless, incredibly impressive. Even with mild flares I'm still exhausted all day with bloody diarrhea. Just to give some perspective, with a severe flare, I would use the restroom 30-40 times a day and it's always just pure blood coming out, I would be incredibly fatigued throughout the entire day, and I had severe stomach pain to the point where tylenol and other painkillers were doing nothing. I was pretty much just a corpse at that point and would just lay in bed.
I don't think GSP will be coming back. The medications you have to take to stay in remission do irreparable damage to your body. But there are other athletes who have overcome similar diseases like Larry Nance Jr. So we'll see.
That's a rough go, dude.
Just to give you some hope, I'll tell you a little about my experience. I was diagnosed with Colitis at 20. After having very bad flare-ups (much like what you're describing) for around five years, and with no true breaks of remission or even near remission mixed in there, I finally decided to bite the bullet and have a colostomy. The surgeon, though, wanted to do a little more testing first, after which I was told that I more likely had Crohn's that was just manifesting itself in the Colon. So I was advised against the surgery, because Crohn's can move (you cut out a piece of your intestine, only to have the flare up migrate to another piece).
So I went on living like that for a number of years. During the week, I ate one meal a day, at the end of the day, because eating during the day put me entirely out of commission. Spent most of my time dehydrated, too, for the same reason and because my Colon just wasn't doing it's job. Stayed home near a bed and a bathroom all weekend every weekend.
And then one day, out of no where, poof. It was gone. I've been in full remission now for 8 years. I've not had a single flare up. Nothing even indicating that it was every anything I struggled with. I don't have any good ideas as to why it happened (I have some guesses, like the fact that I was eating a lot of squash and broccoli and was on a kick for "super foods" at the time... but that kick didn't last, and I'm still good; or the possibility that as I got older, my immune system weakened, and the inflammation finally just died down). But in any case, it happened. Fully, and completely. I got my life back.
I really hope it happens for you.