On the companion quest, Striking At The Heart, and Aela has directed me to Valtheim towers, however the Silver Hand leader im supposed to kill is already day (no doubt by my doing), and is marked as a 'Bandit Chief' so the marker points towards his corpse but i cannot do much else... will the body reset sometime so i have new enemys to kill to complete the quest?

Well I believe the reset period for exterior dungeons is 10 days so you could try that.

Ah, ill attempt that..

had the problem in 1st playthrough and my current one.In the 1st game i found a vast cave later on with a ship inside a large cavernous area The quest reset there and i killed the leader. Wisk i could remember the name of the cave, but i don't. I believe it was quest driven but not sure