Don't let it get you down, Mary. The Sapphire is a great ship (by far, my favorite)! I'm sure you will have a great time regardless of the dining situation. We were disappointed that the whole family couldn't sit together, but when you consider that dining is such a small fraction of the total cruise, it really wasn't such a big deal. There are plenty of other opportunities to meet people onboard and you can still sit with others at a smaller table for 6, which may give you an even better opportunity to really get to know your tablemates.
And, like I said, I'm not 100% sure that their weren't any tables for 8. It's just that I didn't see any and they wouldn't let my family have one, so I'm assuming that there may not have been any.