from what I could understand, you are worried about the hollow area you see in the x ray
of extraction area. Well, since the roots of the teeth are embedded in the jaw bone, there will be an area of hollowness which you will see in the x ray taken immediately after extraction. Normally this area immediately fills up with blood and is gradually replaced by bone which may take 3-6 months. An x ray taken after 6 mths will not show that hollowness. Therefore if there is no pus discharge, pain
or swelling in the operated area just
relax and give the body some time to heal itself.
Regarding replacement of tooth, there are a variety of options available to you including dental implants
with their suitable cost. You will have to discuss that with your local dentist.