The problem is that the Z10 and Q10 are 2 years too late.
So was Windows phone. But (sadly) that is recovering, so why won't BB?
There are lots of parallels between Nokia and BB.
They were both big and lost share.
They both replaced their smartphone system with one missing features. (Both systems needed something done, I think BB needed to replace theirs, Nokia didn't, another overhaul would have done the job.)
They both alienated users with their new system. (By replacing it for Nokia, by being too bloody slow for BB)
They both let down adopters of the new hardware with system upgrades. (WP7 phones not going to 8, playbook not getting the new system)
The new systems both weren't a good fit as a replacement for the old one. (WP is more like iOS, Symbian is more like Android with the app store system. The new BB drops BIS and BES won't work without upgraded servers, so is more likely to appeal to ex symbian users than ex BB users.)
So if BB brazen it out like Nokia did, they may regain enough market to survive, even if it's not at the same level as they were at.