He says to George, 'Come on, George. Me an' you'll go in an' get a drink.' This could show that all is not lost for George, as Lennie seems to be immediately replaced with Slim in the scene where Lennie was shot and then Slim comforts George. This all makes it seem like although Lennie is gone, George has found a new friend in Slim. This is also shown quite clearly when they walk, together, up to the highway. The highway could represent a new start, because a highway takes you from one place to another, so the fact that George is walking up to the highway with Slim could show that George will have a new start and will have a close friendship with Slim now that Lennie is gone.
This would be good for George to have Slim as him friend (or travelling companion) because slim is a skilled worker and could get a job anywhere, he is reliable and is a normal person. This would mean that George might be able to buy his farm with Slim and he could still achieve that dream and that the dream didn't die with Lennie.