I suspect most of the value in a gold ring is in the working rather than the weight of the gold. Hope you don't get too disappointed at the value placed on them when you do opt to sell.
of-course you should get your stone return if you selling only gold. In this case buyer will check the purity of gold by getting stone out from ring and then weight it. And will calculate the price accordingly.
You need to ask buyer about that before you sell the item about their policy.
And if you sell ring with stone then you should get the cost of stone too.