Single parent blue tit

We have been watching a blue tit building her nest in our camera box. Initially the male was frequently around, popping into the box from time to time. However, we haven’t seen him for a couple of weeks or more. The female laid one egg a week ago but no more since then. She spends short periods on the nest and then leaves, and she roosts there overnight. What are the chances of her incubating her solitary egg and raising a chick alone?