Worse than that, comebacks almost never happen in the business world. Apple is actually a very, very rare exception in that way.
Once blackberry shifted to servicing their existing users and not adding new users, they were already dead. This was long before the BB10 came out. You can see it plain as day in their sales charts. Articles were written about it almost two years ago.
The only way to reverse such a trend is to come out with new products that drive a Huge waver of adoption and generate new customers. It's arguable that even the BB10 sales (3 million units?) are similarly just maintenance for their existing faithful customers but even if some of them are new customers (let's say half), that is still a drop in the bucket. It means that since about 2009 or so, Blackberry may have added a few million new users tops, while iPhone has added maybe 100 times that.
They are doomed now just as they were already doomed before the BB10 became available. A great deal of the reason for finishing and selling it, is to make the hardware side of their business more attractive for a takeover or a sale. Anyone with any business sense could see the writing on the wall for the company as a whole for a long time now.