We are planning to "practice" a lot before our cruise.....taking her to noisy restaurants, lots of stroller rides, making sure her sleep and eating schedules are going to work with our activities etc.....
I can't think of too many situations on the ship where it is very quiet, and a babbling baby would ruin the mood. She only cries for a few minutes at bed time, so we should be fine.
I think my only time for a few drinks and some blackjack will be late night, when the baby is sleeping with Grandma.
My 6 hours at the pool on the "fun days at sea" will probably be cut to 1-2 hours during nap time.
You should be ok, as long as mom and dad are planning on including the baby in activities and keeping her happy, and not just dumping her on the grandparents the whole time.