Welcome, though I am so sorry it is under such sad circumstances...
I would think, if the stitches were in for at least a week they should have been fine at removal? Though if the incision was large, like, *much* larger than a female cat spay incision
, that could have been a factor in the integrity of the incision healing process. Also, if the kitty groomed and worried at the incision site after the stitches were removed, that could have also been a crucial role in the failure of the incision site. How soon after the stitches were removed was he found in that condition?
What a horrible, horrible thing to come home to. I cannot imagine.
I would agree with the vet, these things can happen, but only very
rarely. Without knowing more I cannot condemn this vet, though I think due to the traumatic nature of the cat's end, it would be a very kind 'goodwill' and humanitarian gesture on her part if she refunded all costs associated with the neutering surgery.
I am so very sorry for your nephew and his kitty.