What are the typical complications in late dental implant?

Your concerns are valid. However, there should be no expectations of any guarantees from a doctor about treating a medical condition. Several factors can play into the success or failure of a specific procedure including the GBR and implant in your case. If you are concerned about a failure it would be best to discuss this with your dentist prior to embarking on any treatment process. The number one thing in my opinion would be for the patient to be in absolute understanding of what they are getting into and what are the possible risks and complications from such procedures.