What is the ruling on abandoning friends in the three situations mentioned, and what are the consequences for someone who has been abandoned but was not the initiator of the abandonment, based on the hadith "Whoever abandons his brother for more than three nights, and dies; he will enter the Fire" and the hadith "The gates of Paradise are opened on Mondays and Thursdays"?

There is no sin upon you if you were not the initiator or cause of the estrangement. However, it is advisable to respond to harm with kindness, acting upon His (the Almighty's) saying: "Repel evil with that which is better, and thereupon he between whom and you was enmity [will become] as though he was a devoted friend. But none is granted it except those who are patient, and none is granted it except one having a great portion [of good]." (Fussilat: 34-35)