Is severing ties with one's brother considered sinful and deserving of God's curse, even if the reason for the estrangement was the brother's injustice and his striking of him in front of his wife based on her words?

What the brother did by unjustly striking his sister is wrong and an injustice. We advise the sister to meet ill-treatment with forgiveness and pardon, for Allah Almighty says: "So whoever pardons and makes reconciliation - his reward is due from Allah. Indeed, He does not like wrongdoers." And to maintain kinship ties, one can seek the help of someone who can clarify the matter to him and prove the sister's innocence of what was attributed to her.