Highly unlikely for same reasons that the 2003 protests didn't result in a crack down. The rest of the world (especially business) actually cares about Hong Kong. It'd be economic and political suicide to send in troops.
The government backed down in 2003, which is why this could be different. Unlike 2003 when China was still emerging, China is now legitimate and increasingly assertive superpower. China is now much more hawkish than it had been in the past. This is also a new government.