What’s the risk involved in buying Twitter at the current price? Isn’t that a guaranteed 10% gain?

If Twitter is set to sell at $54.20 per share, that's a 10% gain from the current price. With that being the case, why isn't the price already hovering around this mark? Is there still a chance the deal doesn't go through?

Just wondering, because it seems like a no-brainer arbitrage opportunity but I feel like there must be a catch. Thanks for the answers!