This is so sad,you did all you could,and stayed with him and loved him at the end.I am glad you did not leave him at the vets.
The condition the vet mentioned was an ileus which occurs when a piggy has not eaten for a while.It is not just a post op complication,it can occur with dental problems if the pig is not syringe fed.
You were very unlucky with Squeak, but I suspect ,once again, UVS,sadly this seems to be popping up more and more on the forum.
Hugs from The Epsom Mob