I would like to think that Dan decided it was all a fool's game, and is now taking classes for his degree in English Literature at Oxford, wanting to be in a sane location, with money he took from hidden accounts Natla had set up. He doesn't have to ever work unless he wants to, and sends Jon a Christmas card from mail forwarding services across Europe so he can't be easily found.

Edit: after a bit of thought, I expect Jon has the resources to find Dan, but is respecting his desire to be left alone unless things go crazy and he really needs Dan's help. The entire mail forwarding thing is Dan's way of requesting privacy without being rude.

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Geoff Depew - Darth Mephron
Haberdasher to Androids, Dark Lord of Sith Tech Support.
"And Remember! Google is your Friend!!"