For many investors, a large portion of their investments are held in 401(k)s, IRAs, or other tax-favored retirement vehicles. While these accounts can be ideal for sheltering retirement savings from taxes both preretirement and post-retirement, they can also be highly vulnerable to tax losses in an estate, if they are not bequeathed properly. For instance, a $1 million IRA inheritance could be whittled to almost nothing under worst-possible circumstances, such as a combination of estate...