Basically, one of the reasons why I was wanting to do this was to make a more "adventure mode friendly" world. I wanted to make some inhabited forts for the adv to visit. The same empty forts were starting to drive me crazy, and was eventually the reason why I started playing DF mode in the first place. I want to explore my forts now with my adv, but eventually without abandoning them, which I assume will be quite an undertaking.
Did you try out my instructions at the link above (using DFusion and dfhack)? I started out the same as you - I wanted to "retire" a fort without having the people leave. I was somewhat successful - I ended up with a fortress with all its people still living in it, and responding properly to conversations with an adventurer (i.e. they properly give directions when you ask them about "Surroundings" which means they consider the fort their home). The fortress behaves as a normal Mountain Hall - I was able to retire adventurers in it.
Plus as a bonus, if I reclaim, I still get all my old dwarves and retired adventurers as "Friendly" units on the map.
I'll repeat the instructions here:
1) use DFusion->Tools->"Prevent items from scattering" on your paused fort.
2) use DFHack's dfmode.exe to switch to "Adventure" and "Direct Control" - this will switch you to Adventure mode
3) use DFusion->Tools->Change Adventurer - it will put up a list of units on your map. Pick a dead goblin, or whatever, as long as it's dead.
4) without unpausing, save the game (this means don't go back to the dfusion window before saving)
5) quit DF, restart, and load the game. You will be in Adventurer mode, and the screen will say "You are deceased"
6) press ESC, Finish Game
You will now be at the main menu, and if you check Legends mode you will see your fort is still in the game world, with all its inhabitants alive (but pets will die unless you do some other stuff). You are now free to start another fort, or play an adventurer.
I'd be interested in your results if you try this out - I only figured this method out for the first time last night, and I don't know what other bugs this can introduce to your game world. Still from adventure mode it looks ok.
To put it most simply, you cannot leave a fort intact while you do something else.
To put it detailed, you can, if you use DFHack to swap game modes. This can will have unexpected results, as this is a HUGE change to game working and is pretty much guaranteed to break something. But in theory, if you start a fort, then hack yourself into an adventurer, then quit as that adventurer, the fort may or may not remain intact. This is uncharted terrain though, no one has seriously attempted this. Or at least, if they did, they didn't brag about it on the forums.
Yeah dfmode came out two weeks ago I think, and there are only a few of us playing around with it. The new thing I found was to swap yourself into a DEAD entity, so it goes immediately to Finish Game, and no extraneous buggy adventurer data is saved back to the game world. I'll be playing in this world now, try to see if I broke anything else.
I've been trying to swap into a live dwarf now, with not much success - using a fortress dwarf as an adventurer looks like it's missing some data (can't retire anywhere) but I may just need to play around with some flags in Runesmith. I'm also going to play around with adventurer->fort mode in the next few days.