Hello, and thanks for writing in. I'm so very sorry for the loss of your cat.
From your description, and from what I have seen with many deceased cats over the years, I would say he was most likely hit by a vehicle.
Many times there are no external injuries, but there are internal injuries, and the only thing you may see is blood coming out from the mouth like you mentioned.
What you are describing (the bone sticking out a bit) could be consistent with a broken bone (i.e. leg, shoulder blade).
It's possible that he was hit, then walked/crawled to the spot where he passed away (where you found him).
When animals pass away, their eyes typically stay open, no matter what caused them to pass away. The tail being curled up it not a specific thing that is seen when a cat passes away, so I guess it's hard to say for certain why the tail was curled up.
The paws being crossed is also non-specific and may have just been the position they were in when he passed away.
From your description, I would venture to guess that he was there anywhere from 2 or more hours, as the things you are describing can all happen in that time frame (or of course longer).
Maggots typically can show up within 2 days after flies lay their eggs.
It's possible that he was alive for a short time after being hit, but I doubt is was very long - possibly minutes at the longest most likely.
You're very welcome - glad to be here to help. Again, I'm very sorry for your loss, and you'll be in my thoughts during this time.