Pilot reported a loss of electrical power and engine power. An immediate landing procedure was started at an airport. As the aircraft touched down; the main gear collapsed and at about 20 kts.; rudder control was lost. The aircraft depart the runway into soft turf.

Narrative

Electrical problem whereby entire avionics system and engine lost power temporarily; then intermittently until landing. Headed straight in to ZZZ. Configured aircraft for best glide. Initial thoughts were battery/alternator problems (Have 2 Alternators and 2 Batteries); but avionics were in the process of rebooting so could not observe Voltage/Amperage at first. Avionics rebooted; and began emergency procedures: Battery Voltages Green; Alternators producing voltage/amperage; all Circuit breakers in; switched to ECU 2 (backup ECU) and Fuel Pump 2; switch fuel tanks. Radios came up; called into ZZZ Unicom and advised local traffic that I was having problems and coming in on a right base for Runway XX. Noticed there was power lines running across my path to Runway XX; observed to ensure clearance. Resumed diagnosis; and deduced might be the Electronic Bus Mgr. upon which time engaged the Emergency Bus Bypass switch which routes direct power to the Buses. Reached over and Pulled RPM control (Prop pitch) back to reduce drag and began slight turn to line up with Runway XX once Power Lines were cleared. At 300 ft. AGL; had runway made and continued reduced power descent. Dropped landing gear; received Green Light on Nose; but not Mains. Was now at about 50 ft. AGL and just about to cross threshold. Pumped emergency gear pump a couple of times and noticed the Emergency Bus Bypass switch was back in the off position. Quickly flipped it on again and dropped full flaps. Engine began to come alive again and thought for a moment that I should do a go around and work on gear; but decided that I had runway made and wasn't sure that problem was totally fixed. Decided continued landing was smartest/safest bet.Touched down at 65 kts.; soft landing; but Mains had not locked out and retracted back into wells. Nose Gear remained down and aircraft settled on rear tie down skid under tail. Shut engine down to avoid prop strike if Nose Gear happened to give way. Continued down runway with no braking (brakes are on Mains) and limited rudder authority. As aircraft slowed to about 20 kts.; lost rudder authority and aircraft slowly veered to left side of Runway XX and came to full stop about 25 ft. in soft turf at which point the nose gear retracted and aircraft sat down on belly.Damage incurred:Minor repairable abrasions on belly and Tail skid section.Nose Gear Hydraulic Cylinder brokeOne of Three prop blades damaged when nose gear retracted at stop; unrepairable remaining blades and hub no damage.Time from Occurrence to landing = 3 mins