All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
We would like to inform the questioning brother that it is not permissible for a husband to be absent from his wife for more than six months. Abdur- Razzaq narrated in his Musannaf that “‘Umar Ibn Al-Khattaab asked his daughter Hafsa [the wife of the Prophet how long can a woman bear the absence of her husband? She replied: “Six months.” ‘Umar used to not keep a Mujaahid husband from his wife more than the above period.”
In fact, this is among the merits of the Sharee'ah because it always aspires to protect a woman and a man from deviation.
A husband is responsible to provide his wife with means of living, lodging and the other necessities in reasonable terms. It is narrated in Sunan Abu Dawood from Mu'aawiyyah Ibn Haydah who said: “I asked the Prophet of Allah: “What are the rights of a wife on her husband? He replied: “Feed her when you feed yourself, clothe her when you clothe yourself…etc.”
Based on the above ruling, it becomes clear that the absence of your sister's husband till two years without having her consent, besides neglecting her expenses, then both acts are not permissible if she does not agree with them. She may sue against him in an Islamic court or a substitute for it; e.g. Islamic center, in order to consider her case, solve her problem, and get her rights. In spite of the above practice, the marital ties remain without any change till the husband divorces her or she takes a divorce through a judge. However, if she is patient, and there is no harm for her, then it is better.
Allah knows best.