Is my shunning of my wife's father, who insulted and threatened me and my family, and who underwent surgery a week after his deed, a correct action in Islam? And what is Islam's ruling on his deed?

It is better and more rewarding to forgive the wife's father, to show kindness to him, and to visit him in his illness, because a Muslim is required to repel evil with good. This demands patience and a desire for the immense reward, as Allah Almighty says: "And not equal are the good deed and the bad. Repel [evil] with that which is better, and thereupon the one whom between you and him is 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]." It is not permissible to abandon the wife's father or to boycott him, for the Prophet, peace and blessings be upon him, said: "It is not lawful for a Muslim to abandon his brother for more than three days." As for his unjust cursing of you and your family, it is not permissible in Sharia, and its sin is upon him, for the Prophet, peace and blessings be upon him, said: "Cursing a Muslim is a transgression, and fighting him is disbelief."