You know how it is. You're building happily, and then UMIGOD A FORGOTTEN BEAST COMES AND KILLS HALF YOUR DWARVES and ruins your day causes Fun. Or maybe some dwarves get killed in a siege that you barely held out from. The option that most of us face is simple abondment, and then coming back, or perhaps just starting a new game all together. What I propose is instead of leaving all your dwarves and everything, you can move. So you can keep (most of) your dwarves and (most of) your animals and supplies, to go to a new location.
To haul all these things you would need wagons, and a 'wagon pulling' animal (horse, mule, etc and each would have a different speed and carrying capacity). Wagons would require 3 wood to build. Perhaps it could be similar to adventure mode that while on the move, your dwarven caravan *can* be attacked, by wild animals, and possibly goblins (or peeved off goblins/humans/dwarves). It would take a certain amount of time to reach the place that you're going, and you would need enough food and water/booze to get there. But once there you would have your old gang, a (possible) veteran military, and your legacy as (enter dwarf civilization name here) will continue with your old fortress people!. Plus this way you could try and loose the enemy for a while (That is until they see you with scouts and what not).
And then possibly you could reclaim your old fortress if you wanted. This way you would be much more mobile ^^. It's a little ambitious, but I think it would a whole new dimension to the game.
What do you think?