George Eliot's The Mill on the Floss essentially ends with the deaths of Maggie and Tom, but there is one short epilogue after. The purpose of the epilogue is twofold. First, Eliot wants to show how life, particularly nature, moves on after death; anyone who encountered the site of the flood five years later wouldn't even know it happened.
Nature repairs her ravages—repairs them with her sunshine, and with human labour. The desolation wrought by that flood had left little visible trace on the face of the earth, five years after. The fifth autumn was rich in golden cornstacks, rising in thick clusters among the distant hedgerows; the wharves and warehouses on the Floss were busy again, with echoes of eager voices, with hopeful lading and unlading. (Conclusion, para. 1)
This theme of nature's indifference appears throughout the novel and also in many of Eliot's other works. The flourishing mill seems almost cruel in contrast to the experience of Mr. Tulliver and the impact his death had on his children's lives. But now, all of the Tullivers are gone and the flourishing mill is independent of their struggles.
The second purpose is to show how humans move on after death, though we are less indifferent than nature. The epilogue says that two visitors come to visit Tom and Maggie's tomb, "by two men who both felt that their keenest joy and keenest sorrow were forever buried there." We can easily conclude these men were Stephen and Philip, with one of them presumably paying for the memorial and still feeling the raw emotions of the loss of Maggie by the time they first visit. However, one later visits—with "a sweet face beside him," either a wife or child, and the other never visits again, sticking to the forest "where the buried joy still seemed to hover, like a revisiting spirit."
We can conclude Stephen is the former, who visits twice, suggesting that he still thinks of Maggie but has moved on like nature. The latter is Philip, who feels the loss, Eliot suggests, for the rest of his life, in contrast to nature's ability to regenerate.