Do you know where the aneurysm is located? That makes a big difference, ascending or descending (thoracic or abdominal in the case of descending). Abdominal aneurysms are the “easiest “ to treat since stents can be used, ascending are more complicated since open heart surgery is the only method. In any case, at 5.0cm he should be in the hands of a very experienced surgeon (different specialty depending on where it is) and a cardiologist who specializes in aortic diseases.

The surgeon would be able to weigh the risk of surgery against any other health issues he may have, but again at 5.0 cm he should be seeing one ASAP. Medicine has come a long way and the risks of surgery have come down, of course are not 0 and they depend on general physical health and comorbidities, so he should not think this is it for him. But if he is dealing with dementia convincing him may be another issue.

You are in the right forum, we all have gone through the process and can at least give you advice .