Does she have to sell the house or buy him out?
If she wants to retain the house, she will need to buy out his financial 'share'... If she is not able to do that, either by payment or loan, then the husband may opt to buy out her share, or the place will have to be sold & the proceeds divided either by agreement or court order....
If the marriage cannot be saved & they do separate & need to settle property & finances the best way of getting an accurate idea of each parties 'share' is to see a family law solicitor with all the facts, history & finances of the relationship, because those circumstances & others can have a significant influence on each persons 'just & equitable' share.