He is shaken. That won't be fixed overnight and a lot of the change will need to come from him.
We can offer no assurance the seal won't take it. To anyone. We've all lost people to it. We will likely lose more. Only finding a way to accept what you have now will ease that. He worries about what ifs.
As for food that should improve with his mental state. It is provided to him, so it company but if he refuses he won't die. He will be weakened but he knows that. It's a symptom of his distress.
There are no promises we can give about staying. We can only say 'I am here now' and encourage him to take that gift.