Let me explain it to you. A teacher/copper/fireman/street cleaner who's been with the city of Detroit for three years, has accrued 3 years vesting in any contractual obligation. Fifteen years tenure? Fifteen years of accrued financial benefits. That's what the constitution says.§ 24 Public pension plans and retirement systems, obligation.
Sec. 24. The accrued financial benefits of each pension plan and retirement system of the state and its political subdivisions shall be a contractual obligation thereof which shall not be diminished or impaired thereby
What it doesn't say is: "From your hire date and forever onward, new contracts changing the pension plan don't apply to you."
Pay people their accrued benefits and carry on. Put them on normal Social Security like the working stiffs they serve enjoy. Or give them a 401K with a maximum taxpayer contribution of, say, 5% along with their Social Security. Those that the fund can't afford to pay off? Well, taxpayers are stuck with those. Right after the politicians who failed to fund them properly go to jail.