This game has 4 layers of randomness, so the replayability is certainly there.
1) The starting tokens are fairly random. Tzeentch likes Warp Stones, Slaanesh likes Nobles/Heroes, and the Horned Rat will like Skaven tokens. Each of the 9 regions will receive some token to start, and only 2 of them benefit no players. Khorne is very interested in eliminating opposing figures, so working with the randomized tokens, the first round is certainly up in the air (though it's still realistic he'll get no kills whatsoever that round).
2) The Old World cards can impact the game severely, especially the new ones coming up. You never know what's going to happen, and it can cause players to drastically change their previous plans.
3) Each player's Chaos decks add to the randomness, simply because you never know what capabilities your opponents have. I've won games because I accurately called that an opponent did not have a certain card in their hand. Tzeentch's Teleport card alone makes a Bloodthirster in the Empire a good opening move.
4) Of course you also have the battle dice. Khorne's the only player who can have all the skill in the world and lose due to the dice. What figures die has a huge impact on the game.
Don't get me wrong, this game is plenty strategic. It's far more strategy than luck, but with these 4 elements to it, it's got plenty to make the replayability high.