Despite a tentative agreement to reduce long-term debt, Fitch Ratings on Friday downgraded West Penn Allegheny Health System’s bond rating to C from CCC. “Fitch believes that a negotiated debt restructuring appears to be inevitable to forestall insolvency, given WPAHS’s financial deterioration and the failure by WPAHS and Highmark to complete a proposed merger,” the agency noted in remarks that accompanied the downgrade.