This is all a bit of guess work and deduction,
Its looks as though it was still in velvet when it died and,
This year the fallow in the park did not start to cast until I came down to Quex, this would mean had it died then it would have had no antlers,
the antlers look fairly well developed but depending on area I may well be wrong!
Last Aug a muntjac was knocked over on the track down to the house I left the carcass on the verge to see now quickly it decomposed It took less than 2 weeks to just be skin and bones.
My guess would be less than 6 weeks.