Residents didn't directly sign up for these debts. A series of corrupt Democrat politicians who used theses pensions to buy union votes are responsible. While I admit the thought of their personal assets being seized to pay off these obligations does make me smile, I also don't think that'd be legal.
Similarly, it's not the personal assets of the rest of the citizens of Illinois that would be at stake here. There may be an argument for the sale of public assets, owned by the State itself, to cover some part of this in a bankruptcy hearing but I'd imagine there is going to be significant legal challenges to that as well. The optics of literally selling our children's public inheritance to pay off these corrupt deals is not going to play well with the electorate.
The counterparty for these pensions is not the individual residents of the State. It's the State itself, and possibly a subordinate institution. Sinking funds for current employees of those institutions are fair game. Similarly, the rest of the country is not responsible for these debts either.