To those saying 'what else could he do to stop the try' as an excuse, does that mean in a try scoring position, if you can't stop the man with an arm, you're ok to trip? Or if you're a tiny fullback with Nelson Asofa-Solomona charging at you right on the line, 1 on 1, you're ok to jump up and forearm him in the chops?
Regardless of where on the pitch, or under whatever circumstances, the tackler has a responsibility to only attempt at legal tackle. If the play cannot be stopped with a legal tackle, resorting to foul play is not an option, and should therefore be subject to appropriate disciplinary action.
Slater 100% forcefully led with the shoulder, arm tucked and therefore 100% should be charged. But as much plenty of others, I'm also pretty damn sure he'll get off using the most tenuous of loop holes.