What is the ruling on sleeping just before the Maghrib prayer until one wakes up after its time has passed, and is this considered an act of disbelief that necessitates uttering the Shahada, and must the prayer be made up?

Intentionally delaying the prayer beyond its prescribed time is not an act of disbelief that expels one from the fold of Islam, according to the majority of scholars; rather, it is a major sin. Your sleep after the prayer time has begun is forbidden if you predominantly believe that you will not wake up until after the time has expired. However, if you predominantly believe that you will wake up before the time expires, then it is not forbidden. Your prayer is valid and does not require repetition. You are not obligated to pronounce the Shahada (testimony of faith) nor perform ghusl (ritual bath), but you must repent to Allah if you intentionally slept until the time expired.