"This," said Reepicheep, "is where I go on alone."
They did not try to stop him, for everything now felt as if it had been fated or had happened before. They helped him to lower his little coracle. Then he took off his sword ("I shall need it no more," he said) and flung it far away across the lilied sea. Where it fell it stood upright with the hilt above the surface. Then he bade them goodbye, trying to be sad for their sakes; but he was quivering with happiness. Lucy, for the first and last time, did what she had always wanted to do, taking him in her arms and caressing him. Then hastily he got into his coracle and took his paddle, and the current caught it and away he went, very black against the lilies. But no lilies grew on the wave; it was a smooth green slope. The oracle went more and more quickly, and beautifully it rushed up the wave's side. For one split second they saw its shape and Reepicheep's on the very top. Then it vanished, and since that moment no one can truly claim to have seen Reepicheep the Mouse. But my belief is that he came safe to Aslan's county and is alive there to this day.
From The Voyage of the Dawn Treader. Compare A Strange Poem for "the Mouse is a creature Of great personal valour", and Pilgrim's Progress - Crossing the River for the passage to heaven by water.