SW is absolutely suitable for long-term mainenance of your weight loss as it's essentially just a healthy eating plan and is so flexible that you can adapt it to whatever your lifestyle is.
Syn values can and do change as manuafacturers make changes to recipes or as new products come along. As a target member, as long as you stay within three pounds of your target weight you can go along to class for free. You would have access to any announcements about changes to syn values there as well as getting the password which allows you to look up syns online. Continuing to go to class is a very important part of maintaining, even if you don't go every single week, and useful for helping you to keep on track. You usually find that those people who stop going do put weight on again without the support of the class environment. However, if you don't want to go to class you can buy a syn directory with lists of syn values, although this is only accurate at the time of publication. And don't forget you can come here for syn questions!