This may make Washington and Ottawa feel good (Because it lets both sides save face), but is going to be pretty shitty for the people living in said territory, if it ever goes back to being split.
If it will never be re-split, then it's a de-facto annexation. In which case, I'd prefer that the residents vote on it.
If it will never be re-split, then it's a de-facto annexation. In which case, I'd prefer that the residents vote on it.