The affairs of the one who trusts are entirely in the hands of the one in whom he trusts. No one else can harm him or help him do him good, or shield him from injury. As in the case of a slave confined to a prison under the control of his master. When the one who trusts is in the power of the one in who he trusts in this way, trust in him is more fitting. pg 369
Daily Halacha
There are two exceptions to one returning to the place he ate to bentch
1. If by the time he will return to the place where he ate more than seventy-two minutes will have passed from the time he finished eating, he should bentsch immediately and not go back
2. If there is bread available at the place where he presently finds himself he need not return to the place where he ate originally. Instead, he should wash his hands without reciting al netilas yadaym, recite hamotzi, eat at least a small amount of bread, and then recite birkas hamazon.