Best is to have some sort of ending which actually is not the end. Like starting over (with acknowledgement that you completed the game x times, bonusses, new type of gear, access to new features of the game etc), or a portal to a new world with a new set of rules when it comes to levelling, but perhaps also other aspects of the game.
And ending should feel like your final goal, so you keep motivated to reach it. Though I am afraid that 2800 levels will already be to much for many starting players.
Another way can be to totally distract players from the levelling part, by having tons of things to do, or do just the opposite and fully focus on levelling, but to keep players motivated reward them for new levels gained, though in the end, that may become boring aswell if it are just the same old rewards all the time.