Houston-based Key Energy Services Inc. and some subsidiaries expect to file a prepackaged Chapter 11 plan of reorganization by Nov. 8. The restructuring is expected to reduce Key’s debt by $725 million to about $250 million. The onshore, rig-based well-servicing contractor plans to begin Chapter 11 proceedings in Delaware once senior note holders and lenders officially vote on the plan and an $85 million rights offering expires. Key plans to continue paying employees, vendors and trade creditors…