I an assure you not many jewellers would be bothered to tak eout stones from a ring and replace them with inferior quality stones !!! As mentioned, unless they are maga quality diamonds, you would get a scrap value for the ring, based on weight as the gold weight is more than the stone value you will come off better off. Unless it is a fantastic ring, youi shouldn't have to get an insurance valuation as most policies allow you to specify items up to £2000. If you give me more detail of the ring, I can tell you roughly what the replacement cost would be.. Check the hallmark - 9ct is 375 , 18ct is 750 this will affect the valueation. You should be aiming for about £9-10 SCRAP VALUE per gram of ring