Could we write in the contract that our county will set aside the housing for 20-30 years (whatever is required based on rehab or new housing) but that only so long as DSH continues to provide treatment funding as is currently being proposed at up to $125K per client up to 18 months?

No. The counties cannot alter the terms of the 20- or 30-year restrictive covenant. However, DSH retains the ability to cancel or modify the restrictive covenant in the event the program is decommissioned and DSH does not have another population to serve in the housing.