When the grid is initially rendered, it follows the ordering of the list (model) behind it. How would one revert to that same natural ordering after a sort by column has occurred?
Within an ng-repeater you could set a custom data attribute to {{$index}}
<li class="sortable" ng-repeat="item in items" data-index="{{$index}}">
Then when the DOM is manipulated to produce your column sort the index when rendered will be preserved within data-index