As bednobs says the property will be repossessed if the mortgage is unpaid but there are also a few further points to consider.
If the property is sold and the equity split between the two parties then presumably the wife will have to then find alternative accommodation and pay rent which would probably be considerably higher than a �23,000 mortgage.
If she remains in the property what income will she have? If she will be claiming benefits she can apply for help with the mortgage after a qualifying period, legally she shouldn't have a problem staying in the property until the youngest child leaves education at which point the husband would be due his share of the property.
If they sell the property and she receives her share of the capital she would then have to use this to support herself/pay rent etc before she could claim benefits (once capital is below �16000.00 can claim at a reduced amount until it reduces further).
They need to carefully consider what to do especially due to the fact that they have a small mortgage and high equity.
Hope this helps?