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It all depends on whether she makes a Will or not- if she makes a Will, the property passes to whoever she has nominated. If she has not nominated someone other than her husband, legally he would have to vacate the property. However, if so, he may be entitled to make a claim against her Estate under Inheritance (Provision for Family and Dependents) Act for insufficient provision and this claim would normally include a claim to be entitled to remain living in the house
If she does not leave a Will, her Estate passes in accordance with the Intestacy rules, which means her husband will more than likely inherit the property (if it is worth under £250,000) and therefore be entitled to remain living there. I attach a link seting out the Intestacy rules-
I hope this assists and answers your question.