Hi sir.... Clinical and radiological ( x _ray) investigation is necessary to rule out the condition of remaining teeth If the tooth is in good condition, it is better to retain the tooth and go for REMOVABLE PARTIAL DENTURE  or OVER DENTURE or IMPLANT PROSTHESIS .... If the tooth condition is not good enough then allow  

Hello Sir, if the remaining teeth are not in a good condition it would be better to get it removed and get a full mouth complete denture. You may also opt for implant prosthesis if possible which is the best available up to date. If the tooth are in a better condition then retaining them is also an option and going for a removable denture or an over denture. All this can be done after having a better understanding of his condition so I would advise you to visit your dentist. And treatment time depends on the type of treatment that you want. ( 2 weeks - 3 months approx)

In order to advise you it is important to check X-rays and also clinical examination is required to check the occlusion. Only then proper advise can be given.