You deal with it the same way those parents who have kids with Leukemia, who die from Sudden Infant Death Syndrome, who are born with a heart malformation, etc etc.
The point is that there are so many things that can happen to kids that can take them away prematurely. CF is by far not the only culprit. But it certainly doesn't make our lives less valuable. And you certainly don't have to reach adulthood to have a purpose for your life.
Your little baby deserves to be on this planet just as much as another baby without CF. And as my wise mom always tells me, the future never turns out how you think it will. You may envision your baby's life to be a certain way, but as you know from life experience, things rarely turn out the way you imagine (usually for the better).
Don't underestimate the powerful, positive impact your child could have on this planet.
And on a side note, I'm generally pretty pessimistic about drug development but PTC124 is one that I'm willing to bet large amounts of money will come to the market and make a huge difference.