I'm sorry about your dad being in teh hosptial. I can relate so much to your story as my dad had the Whipple last June and is now suffering from metatastic disease and chest pain.
If the stomach is paralzed (gastropareis) a J-Tube should be utilized which is a feeding tube that goes directly into the abdomen (or gut) and not into the stomach as a G-tube does. TPN (total parental nutrition using vein to heart method) would be another method to deliver vital nutrients to a person who cannot eat on their own or has a paralzed stomach. and not a G-Tube which goes directly into stomach. If the mucles are paralzed, this type would be of no value to the person and would contunie to vomit their food.
My dad had to have a J-tube for several months following gastroparesis following his Whipple. Sounds similar. Don't lose hope- it can get much better again for your dad-but they need to resolved this right away. My dad was abale to eat on his own again following several months- so I know it can improve so much even when things are so grim. Please hang in there and keep proactive on helping your dad receive optimal care that he deserves. Take care