To answer this question, take a look at the closing lines of the story. To save his friend from being violently murdered by Curley and his mob, George shoots Lennie and then leaves the scene with Curley. As for Candy, he lies down in the barn where Curley’s wife was killed and covers his head with some hay. So, in response to your question, Steinbeck does not directly address the issue of George and Candy buying a farm.
However, if we read between the lines, we can infer that George and Candy’s dream does not come true. Given that George has left the scene with Curley, it is likely that he continues to work on the farm. Moreover, the fact that he does not leave the scene with Candy also suggests that he and Candy’s friendship may not continue in the same manner after Lennie’s death.
I think the title of the story also suggests that the farm is never purchased. Remember that the title is an allusion to Burns’s poem and implies that sometimes, no matter how hard we try, our plans go awry. This may well allude to George and Candy’s farm, suggesting that although they really wanted to have their own place, Lennie’s death means it can no longer happen.