A nice way to end a fort that's going to long is to trigger HFS and flail about valiantly trying to defeat it.
Elsewise if you find yourself getting bored with a fortress it's always ok to abandon it and start again. Plus if this was your first lasting fortress then you can always take what you learned from this run-through to make a lasting fort that fits your ideals better.
And now if you abandon, the survivors will show up as migrants in newer fortresses you make, if they are the same dwarf civilization.
Which makes me think of a possible exploit- IIRC, when you embark as part of an extinct dwarven civ, you not only get your starting seven, but also 2 migrant waves and a caravan at the first winter are procedurally generated instead of being historic figures. Now, if you abandon after that and start a new fort, will your dudes from the previous fort immigrate after the hardcoded 2 waves?