It's not impossible for them to come back, but it would take a miracle at this point. Or, someone with a lot of money to burn to take the company private. This would give them more time to do whatever it is they need to do to get BB10 out, AND try to sell it to people.
Or, they could give up on the developed countries and focus entirely on developing countries, where they claim that their user base is growing like crazy.
One thing's for sure though: the excuses given for the delays of Blackberry10 aren't ringing true to me. Back in 2011 when they told investors that it would be delayed until 2012, the reason wasn't software... they insisted the software was "ready to go," but they were waiting for good-enough LTE hardware to install it on.
Now the reason is "the software isn't a problem, it's just committing all of the code changes." Which... wouldn't be a problem if it was actually true that the software was "ready to go," as they claimed in 2011.