He may have been killed by wolves or bandits.
Spoiler I once found him dead near the back entrance to Embershard.
His schedule has him leave home at 4am and hunts to the SSW until 7am.
2 bandits are just up the hill and wolves are between his house and Embershard.
It's possible he chased a rabbit or fox and found danger.
Look around the outskirts for his corpse.
Also, check about 20-30yds outside the area where the Whiterun Guards set camp.
He can often be found just standing there before 7am.
Hope that helps