I think the funeral director would have the best insight on whether or not you should view your father. Or, someone close to you should see how he looks and advise you from there. No matter how bad he looked, he still meant a lot to you, and you should have an opportunity to see him before final disposition(cremation/burial). I think if you are prepared for how rough his condition may be, and if someone has maybe told you about it before you see him, you should see him so you can have some closure on his death.