Sympathies.
Strange. I know of many cases where the inedible objects like that have been extracted from fishes' tummies as you described and they lived on like nothing ever happened... cups, holders, guards, thermometers, plastic toys, decorations...
Do you have guesses what happened?
If it's of any consolation: if the suction cup was big relative to the fishes size/intestine diameter, he would not pass it and die. He could have regurgitated it too but that does not always happen.