You can get away with anything, story-wise, as long as you give the players enough rewards. These rewards become hostages which compel the players to stay. Sure, you can leave the campaign now, but then you’ll never get to use this +50 vorpal sword of awesome that glows like a lightsaber and once a day can be used to create 2d8 pieces of delicious candy.
To clear up this continual confusion: This is NOT the last strip. The comic ends on Friday. You’ll know it’s the end. It’ll say so.