On marriage, his will (unless it is made in contemplation of marriage) is revoked. If he didn't make another one after marriage, the estate would be distributed on the intestacy rules which means the wife would get a share (amount would depend on whether deceased also had children).
If they divorced after 12 months, she would be unlikely to receive much at all. It would be classed as a "short" marriage (being less than 5 years). She would be very unlikely to get half.