You think Beijing would think pulling a Tiananmen 2.0 would bring HK into the right track fulfilling its economic role after? I dont think almost anyone, include almost every mainland Chinese would think that way.
If military is involved, economies will crash, hard. Not only HK's economy, a lot of economies will crash. It will be an economic suicide for mainland China. Is there any doubt about that? And that's irrelevant if any western countries intervene or not.
You probably haven't talked to any educated mainland Chinese recently? For the ones who would like to get HK in line and even get Taiwan back, the only feasible way they see is economic dominance over those territories. As a strategy by itself, I kinda agree.
Edit: I dont think PRC depends on HK more economically than emotionally. HK is one of the symbols of western countries invasion 100 years ago. Getting it back has a great deal of emotional value for mainland Chinese. What I see PRC can extract more value out of HK right now is to emphasize the western influence over the protest, making regular Chinese more in line with PRC's world view and values. Anger directed towards other countries rather than introspective is a good thing for the gov if and when there's any hardship inflicted during the trade dispute period.