Damn it i hate logout timers. Please add an autosave feature to these forums. In essence, though I'm not going to pretend to know the coding necessary, and probably monumental at that, would it be possible to run two servers, one in dwarf fortress mode, (though the key problem here is the possibility of having no pause if you wished to implement it. On the one hand, you could let other people take control of your fortress while you're offline. On the other, you're letting people take control of your fortress while you're offline. You might be able to set up particular rules for that player, but to be honest this sounds very difficult to implement in real time, though perhaps with the use of macros or limited pause which only affects those in a certain radius of effect it could be overcome.), and another in adventurer mode starting sometime after and set in a previous era of the dwarf fortress server, in which the events of that server happen alongside the adventurers actions?
This is thought in a sandbox, not necessarily everyone plays but they're people you don't know scenario, and with the actions in adventure mode spiraling off into their own timeline. However, every now and then the world is updated with fortresses from the dwarf fortress server that either embark on uninhabited sites or reclaim old ones.
Ideally, and most batshit crazy of them all, fortresses which are currently active in the adventurer server could be interacted with in adventurer time on the adventurer server by their former owner and/or people who that player allows to on.
Most likely this is an idea for another era, but i'm posting it on the offchance it might actually happen.
In summary, and TL;DR: More interaction between adventurer and dwarf fortress modes in multiplayer, would, though being insanely hard to implement as said in the second to last paragraph, and probably for the whole post, be an extremely attractive prospect.