A friend of mine came to the UK from South Africa in Dec 2016 with her husband, who has an ancestry visa. Unfortunately, after just over a year of marriage, their relationship is on shaky ground

We have done as much research as we can about her options, should they decide to end the relationship, and will be consulting an immigration lawyer this coming week, but I was wondering if anyone had any answers in the mean time please?
1. If the relationship breaks down and they inform the HO of this, will the HO curtail her visa straight away, or let her remain on it until it expires in just over 4 years' time? (at which point she would obviously be unable to apply for ILR)
2. If they do curtail it, does anyone know how long you usually have to leave the UK?
3. Will a curtailed visa affect any future applications she makes in any way, if she leaves willingly, using her own funds, within the time frame given?
4. If the HO don't curtail her visa, will she still be able to legally live and work here until it expires?
Many thanks for any help you can give!