ZOMG, if only someone had suggested that sooner!
Before doing a tear down, I would first check for sludge and run a cleaner through to break up the sludge. Lot's of times sludge can break free, blocking a oil passage way causing the lifter to collapse. Besides, if the lifter "goes" it won't catastrophically destroy the engine, likely, worst case it would wear down that particular lobe on the camshaft, and he would just need to replace the cam and lifters.
ZOMG whats with the doucey response?
I tend to disagree with your worst case scenario. Ive done a few 4.8 5.3 6.0 in the shop for tossed lifters. Most of the time a good portion if the lifter is missing, true you could inspect cylinder, and cam, however if you do not find the missing pieces...your just in a guessing game siutation if the motors going to last/.