Just deserts is a phrase that has come to mean getting what a character deserves based on their morality and their actions. It is a particular theme in this novel, as nearly all the characters can be shown to get what they deserve based on their actions. Dunstan Cass, for example, is a prime model of this. A spendthift profligate with no morality whatsoever, he gets the early death that he deserves after blackmailing his brother and stealing the accumulated wealth of Silas. Godfrey Cass in a sense is also "rewarded" for his actions: his abandonment of his daughter is something that earns him a childless marriage, and the fitting nature of this consquence is recognised by Silas when Godfrey tries to reason with Silas to get Eppie back:
God gave her to me because you turned your back upon her, and He looks upon her as mine: you've no right to her! When a man turns a blessing from his door, it falls to them as take it in.
Just deserts is therefore apparent in the way that Godfrey is not able to have children. Having had one child, and disowned both her mother and the child itself, it is just that he is unable to have children himself or to take back Eppie. Eliot creates a world in this novel therefore where morality is rewarded and bad actions bring with them bad consequences. Even Silas receives a punishment, which turns into a blessing in disguise, when he loses his wealth, and is rewarded instead with something of far greater value.