Hello and welcome.
First let me ask you if you are sure it is a meconium plug or if it was meconium illeus? My daughter had a plug (lower in the colon), wheras illeus is usually further up in the digestive tract. It doesn't really matter. Except there is a much higher coincidence of CF with the illeus than with the plug.
All that said, my daughter does have CF. I remember how unbelievably scared and emotional I was when I was in your shoes. Today, my 2 and a half year old daughter is doing terrifically. Besides the fact that she is petite and has trouble gaining weight, she has had NO other issues since the plug. She takes meds and does treatments but ALL of it (including her enzymes as she is mostly pancreatic sufficient) are done preventatively. CF is not a death sentence for today's newborns. There are great treatments, and medicines and there is huge hope for our kids.
Try not to get caught up in a lack of family history of CF. Most of us around here don't have any either. CF wasn't even a diagnosed disease until the 1930's and even then it was missed quite a bit. And the way the genes work, it may not have shown up. I believe I read that nearly 10 million people are unknowingly carriers of CF.
As for having other CF kids, your chance if both you and your partner are carriers is 25% for each kid, but there are IVF procedures that can minimize the possibility even more.
Welcome and hang in there!!! We all know what you are dealing with.