I left two big pans of roast (about 20 lbs) in the oven at 350 over night - from 3 p.m. to 8 a.m. Is this still safe to eat and serve.
It is safe to eat, but not safe to serve.
Elaboration: Depending on your general cleanliness, there shouldn't be enormous amount of bacteria in the roasts: anything above 100°C (200°F) for an hour is sterilised and if you keep your pans and oven clean (with pyrolysing ovens: easy to do nowadays) it is perfectly safe for you, the dogs, the cat, and any other carnivores generally around the house.
However, it's going to be very dry and not very tasty, so I wouldn't actually serve it to any of my guests. What I would do is grind it up, throw it in your biggest pot, cover it in white wine with some nice herbs, put a lid on top and turn a towel around it (so no moisture escapes) and boil it on very low heat until it soaks up a ton of the wine, then add tomato juice until it becomes tender again. Freeze it in small batches so you can re-use it as pasta sauce...
it's safe, and if it's dry (probably is) I'd try making BBQ out of it - pull it apart with forks or fingers, as pulled BBQ meat is always better, then simmer on very low in a lot of BBQ sauce. You can freeze portions of the meat for later, just add sauce and simmer when you want it.