Your question wasn’t attached to an earlier question so I assume it’s about the arborvitae that died. Don’t put your new tree in the same planting hole unless the root ball can be dug up and removed.  Because your shrubs died before they were established you could replant now and if the root ball comes up use the same hole otherwise move it far enough away so there aren’t any roots in the new hole. Your new tree will need good soil contact to thrive. Dead tree roots can create air pockets and impact the new tree.