The current Wikipedia entry on Spook Country contains the following nugget:
The identity of the old man remains unclear, though context implies that he may be Pattern Recognition's protagonist Cayce Pollard's father, having removed himself from the channels of normal life to focus on disrupting what he sees as criminal elements operating in the United States Government.
This is an interesting speculation that would fit within the principle of Occam's Razor as applied to writing, do not multiply characters needlessly. However, from what we know in the following book with respect to the Ugly T-Shirt, he still has friends in high places and markers to call in. If he had faked his death to protect his family, then he could not resort to obtaining those favors, since two men can keep a secret if one is dead.