Surely you are kidding, Mark? Most of the scrapped decks I've ever seen were in way better condition than that.
If you are an experienced argon-arc (sometimes known as MIG) enthusiast with the right gear, the deck theoretically could be repaired, though it still wouldn't be much good because of the dissimilar grain structures involved. It would also need some minor machining around the left front wheel after welding.
There is a mower parts shop that from time to time sells non-genuine copies of Honda bases the same as that one, for $99 if I recall correctly. Other than that, I suppose you could make it into a sort of paddock-mower by wrapping a piece of aluminium sheet around the missing part and pop-riveting it to the remaining perimeter of the base. I doubt it would stay there very long, and would look so bad that you'd be glad when it fell off.
