A sister severing ties of kinship with her half-brother after getting married
If the reality is as you have mentioned, I say that those who maintain the ties of kinship will be rewarded and
those who sever such ties without a valid reason will be the sinful party. Both parties should communicate and cooperate with each other in Ma`ruf (that which is judged as good, beneficial, or fitting by Islamic law and Muslims of sound intellect) in order to maintain the ties of kinship and fulfill the rights of Islam and relatives. Allah (Exalted be He) says,
Worship Allâh and join none with Him (in worship); and do good to parents, kinsfolk
He also says,
And give to the kinsman his due
Both Ayahs (Qur'anic verses) are from Surah Al-Isra'. Also, there are texts of Hadith, which encourage Muslims to maintain the ties of kinship and warn against severing them. In fact, Muslims should maintain the ties of kinship with those who severs them. The Prophet (peace be upon him) said,
The one who joins the ties of kinship is not the one who repays good with good, but he is the one who, when his ties of kinship are severed, joins them back.
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.