The nearly 400-yr long lifespan of the Qing dynasty leaves plenty of room for indeterminable variables
1) political- as I've mentioned in an earlier post, for a laundry list of reasons (ie inept rulers, corrupt bureaucracy, natural disasters), the Ming dynasty was on its way out for reasons independent of any action by the Qing. As others have mentioned, at the time the Qing entered China proper, there was already a dynamic, capable rebel general, Li Zicheng, who captured Beijing. The Qing entry was actually a military intervention requested by Ming general Wu Sangui. Had the Qing not enterred, Li Zicheng was a solid candidate for new Emperor. If not him, another rebel perhaps. But it's quite certain the bell tolled for the Ming dynasty in 1644.
2) military- I'm not an expert on the Qing dynasty but one thing that struck me was the effectiveness of their military. Keep in mind, the Qing represented China in her period of greatest territorial expansion. I'm sure the Mongols didn't come over when the Chinese said 'please'. Had the Qing not ruled China we might see a repeat of the Song (a militarily feeble China giving ground to stronger border enemies). Since the world entered the modern era where sovereignty was taken more seriously, China might have to sit for considerably less territory than it has today. Heck, we might not be arguing about Taiwan or Tibet.
3) social- we all know repressive autocracy is not a characteristic of Manchu rulers. In fact, that was probably one of the things they learned from the Chinese. As I've written before, I believe anti-Manchu sentiment was a convenient focus for Chinese nationalists in the 20th century. However, as of 1644, there's little reason to believe a native Chinese regime would be less autocratic or more readily embraced liberalism or democracy than the Qing.
Neither was the self-destructive inward-looking policy a Qing invention; that also started with the Ming. After the reign of Ming Xuande, the Chinese disbanded the Dragon Fleet and, in doing so, forfeited an advantage they could've had over the Europeans. We also have little evidence a native Chinese regime would reverse this policy.
In conclusion, racial differences aside, the Qing was quite characteristic of native Chinese dynasties. After all, the Manchus modeled their kingdom after the Chinese. In doing so, they built up a nation stable and strong enough to challenge the Chinese, then eventually take their place as rulers of the Middle Kingdom. They alone cannot be blamed for all the catastrophes that beset the country in the 20th century.