The problem is that damage is a realtive term. It is up to the ICE agent to figure out if it is damaged. If it is relatively know (and has the little "eye" on the passport) then it has the RFID which in theory should still be working. Either way, since he is returning to the States, is probablly middle aged if not older and travelling with his wife, the ICE officer may verify that the passport is accurate and not modified and then allow them through, but he may suggest that he get a replacement depending on how damaged the passport is.