To close this out--the short version:
There is a known issue where Personal File Sharing stops when it is not connected to a network, Apple Knowledge Base Document 107367 (see Kelly's comment above).
In my case, I had my System Preferences/Network, Airport, configured to: By Default Join: "Automatic."
So when I restarted, file sharing stopped because a defined/specific network could not be found (the automatic ain't really that automatic). Ergo, the solution was making the change to: "By Default Join a specific (Pendragon) network."
And all is again right in the Pendragon kingdom.