Given that your flight is in June, it is unlikely that Norwegian will be insolvent by that time. However, unless the AF timing is unacceptable, I would take it without a second thought. The primary reason is that Norwegian does not have interline agreements with other carriers. If your flight is cancelled, you may have a 24-hour wait for the next flight. If AF is cancelled or substantially delayed, AF has interline agreements with most TATL carriers and can rebook you to OAK/SFO on one of them. Perhaps you want the full extra day, but if your goal is to get to your destination, you will do better on a carrier which can meet your needs in IRROPS.