The short answer is that yes, you can have a very decent life in HK as a bachelor for $50k per month.
As PDLM says, you'll be looking at about $6k a month for tax, and $1k for MPF (pension), so about $43k takehome. I'd be looking for something more than $12k for rent - maybe $15k to $17k, leaving you with over $25k a month for food/travel/luxuries. $25k a month isn't going to give you an absolute life of decadence, but as long as you're not going to the best restaurants in town every night of the week, you should be able to live a pretty nice life without worrying about money at all. Again, as PDLM says, that $50k would put you into a very small top percentile of wage-earners in HK as a whole, although it's not an outstanding salary for a high-flying expat.
To put it another way - it's a much much higher salary than the vast majority of the population of HK lives on, but you wouldn't be expecting to live the way the vast majority of the population lives.