C172 pilot reported a rough running engine which resulted in a diversion and successful landing; however; the engine completely failed when power was reduced for landing.

Narrative

During cruise flight; approximately 12-mile NE of ZZZ; the engine RPM dropped from 2300 to 2100. I immediately applied full mixture then full throttle regaining only 100 RPM. I applied carb heat and verified normal RPM loss associated. After 30 seconds I removed the carb heat and did not see a significant change. The RPM remained below normal and was slowly deteriorating. Currently I was heading back to my home airport of ZZZ1 at 2000 feet MSL. I had already tuned in ZZZ Tower frequency to listen to as I had passed their airspace previously. Since the engine was running abnormally and beginning to run rougher; I turned towards ZZZ and contacted them on the radio approximately 10 miles out. I advised ATC and requested clearance for runway XX. Gave souls onboard and time of fuel remaining. While proceeding to the airport the engine began to run rougher; and the best RPM I could get was varying between 1900- 2100 RPM not holding steady. At approximately 5 miles out there was a loud pop/bang from the engine and a large amount of vibration. RPM dropped to 1800 and stayed there until power reduction for landing. While proceeding to Runway XX I noted the lack of landing options in the event of a full failure due to the city extending north. I saw various fields and options if I proceeded to the end of runway XY directly as it was a little bit closer; longer and wider. I announced those intentions to the tower and was cleared to land any runway. Once runway XY was assured I maneuvered the aircraft to align and pulled the throttle back to reduce power. Pulling the power back slightly caused the engine to stop running and the prop stopped turning. A successful landing was made on RW XY and rolled to a stop at intersection 1. I informed the tower that everyone was fine and exited the aircraft. The aircraft was towed to a tiedown spot on the ramp and parked. Current cause of the engine failure is unknown.