Yes: don't let them jerk you around. Make them tell you guys exactly what is going on. Don't let them discharge him without knowing why or what is going to happen afterward. Will they take out his appendix once some of the swelling goes down? What if it doesn't go down? What will they do after the drain is put in? Will he have surgery after that?
Ask questions. Don't let them dismiss you. This is way too important. Be nice about it, but firm.
I can understand why they would be reluctant to operate if his bowels are involved because if any of the bacteria from there gets out, it could be very serious. I don't understand them talking about discharging him.
Good luck. I hope your fiance gets better very soon.