Well, it depends on how old the tree is, Dilly, and how well the roots are holding out. Is he watering the tree regularly and fertilizing it regularly? If not, I would suggest he start doing both. Often citrus will survive for a time, but then start to decline if the tree isn't receiving enough nutrients and water, especially if the tree is older. You'd have to see if the tree has sustained any damage to the trunk or roots, or is suffering from some dieback, which can occur in older trees. Or, even a graft failure after a time. Without photos, it's just a guessing game for us. If you can provide us with good photos of the root area, trunk, a good close up of the trunk where the graft union is, the canopy, close up of the leaves, etc., we can try to answer this is a more educated way.

Patty S.