Since the bubble expands faster than the speed of light, it would not be visible in the CMB. The reason that there should be billions of years left is just a statement about probability. Given that the universe has already lasted for billions of years, it would be very unlikely for it to end tomorrow (in fact the odds would be about one in a trillion). So at the very least the universe should last for at least about as long as it's lasted so far (though it could last much longer).

As I understood the article, the bubble collapses at the speed of light.

If I'm understanding you correctly, you're arguing that since we've had 15 billion years so far with no collapse, then odds are great that we've got billions more to go. My point is that if the bubble collapse is not instantaneous, then we don't actually know there's been no collapse so far.

Actually, no, the bubble is supposed to expand at the speed of light.