Our daughter had a congenital heart defect that wasn't fixed until age 2. She started daycare at 18 months. Our pediatrician assured us that because she didn't have any continuing lung problems, and she was over 12 months, that RSV was less concerning.
In NICU it is drilled into our heads that RSV should be our biggest nightmare - and that is true, when you have a brand new preemie. Once they are past 12 months, unless they have a lung condition, it is a normal part of life. Almost every kid will get RSV by the age of two. It's one of the most common cold viruses. It's an issue with preemies because of underdeveloped lungs, very low birth weight, underactive immune system. Our daughter had several colds the first and second years of daycare, but no more than any other kid. She also had heart surgery in between and we were told to treat her like a normal child. They have to get sick to develop their immune systems.
And while getting RSV is a risk, it's a risk for kids who were full term and have no health conditions, too...and even they can land in the hospital. But most kids who get RSV don't end up in the hospital.
I've never heard to quarantine a preemie a second year, if they were born mid-rsv season. The synagis shots don't build immunity, which is why they have to be given every 28 days. If they are not exposed, they won't build immunity.
You might want to consider an in home daycare or a daycare center where the ratio of kids under two is small. Our daughter went to a center, but she was only 1 of 4 kids in her class room, so there was always someone wiping noses, disinfecting toys, etc....
It'l be nerve-wracking...no doubt. It's VERY hard to send them off to "school". I can still remember my anxiety! EEK! But it was the best thing I did for my little social butterfly. Good luck in your decision.