This morning I contacted Dana Krempels about this - she writes many of the articles on websites that we refer people to.
About 10 minutes after I heard Montana had passed - I received her response - and I am posting it here with her permission.
Dear Peg,
It's distressing that the lesion yielded blood. Can the vet tell if it is attached to underlying tissue, or moving freely with the skin? The location of the lump makes me think: possible hernia. If this is the case, the lump you feel could be a loop of intestine, and that would suggest that emergency repair surgery might save the bunny's life (IF it's a hernia, which is a big IF).
If this is a hernia, and the intestine in the loop is being pinched off, it is life threatening, and no time should be wasted. If the section is already necrotic, it might need to be resected, which is a very dicey operation, and the vet will have to determine on the spot whether the bunny can be saved.
This does not sound like a typical abscess or tumor--and I think if the bunny is already inappetant and lethargic, his only chance might be emergency surgery to address the lesion. I hate to say "there are worse ways to die than under anesthesia"--but in a case like this, I think I have to say it.
I cannot examine the bunny in person to really know what to tell you. But the location and the blood inside really make me concerned that this is something very unusual and possibly requiring emergency treatment to save the bunny's life.
I hope this helps.
Dana
In her response to my update, she also stated...
I am so sorry about your terrible loss. I really wonder if this was a hernia, and if your friend has the heart for it, I would strongly suggest a necropsy for her peace of mind. If it really was a hernia that was constricting the GI tract, there may not have been a way to save the bunny.
I am so sorry. Please feel free to share any of the information I sent you with anyone you think might benefit.
I am going to relock this thread for a bit so that Ali can post a Rainbow Bridge thread where folks can share their condolances - then I'll reopen this one in case there is a need for some medical discussion ...