I would find it extremely unlikely that a mouse (dead or otherwise) would have any effect on your dog eating/drinking out of his dishes. I'd look for another cause altogether.
Some dogs (especially GSD's) are so smart that they can train YOU without you realizing it. Maybe your dog has successfully trained you to hand feed him? I know toilet drinking is pretty common for dogs, b/c the water is typically "fresher" than what is in a bowl on the kitchen floor. Sounds gross to US, but for them? Fresh water. :)
Have you changed anything about your feeding habits with him? Some people feed at set times and then remove anything left over. Some people free feed (leave food out all the time for whenever the dog wants to eat at their leisure). We free feed. My GSD usually will only eat after everyone in the house is gone to bed for the night. If we have guests, she doesn't eat at all, usually. At least the first night.
Maybe if you try putting his bowls in a different location? Maybe somewhere more "private"?
Could be a lot of things. Could be he just trained you guys.
But a call to the vet can't hurt if he suddenly is refusing to eat altogether.
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ETA: So I must have a cool dog, cause she's always had elevated bowls (even as a puppy).
;)