They are worth the try. The worst-case scenario is that they will not integrate into the bone, fail and exfoliate themselves, and the very small defect that they leave (less than 6 mm across and 15mm deep will heal back in, leaving him with a conventional denture. Implants cost the doctors about 400+ apiece, then there is the surgical procedure to put them in, then there is the restorative process once they are in and integrated in the bone. If a lab is involved in making porcelain crowns on them, add another 500+ per implant for that. So it is not such a simple thing. Add to this for radiated patients that they have O2 dives to make before and after surgery which cost money and you can kind of get a feel for where this is going. The upper denture is usually little problem, as I said before it's pretty stable because of the suction formed there. The least expensive way of restoring a lower arch is just 2 implants and some overdenture attachments and a full denture on top. Where implants get really expensive is in the normal population and they are being used to support multiple tooth porcelain bridges.