The two main reasons given for treating perennials as annuals are usually the fact that they won't survive low winter temperatures, and that they won't flower as well the next year, but neither of these are necessarily true.
Temperature of course depends largely on where you live, and if you have below freezing conditions for most of the winter, well then annuals they probably are. But if you are in a milder or more sheltered spot, wait till spring and see what you manage to bring through.
As for getting fewer flowers, I've found quite the opposite. I've got several so called annuals on the balcony which are now into their second or third year and are bigger, stronger and giving more flowers than ever before. Here for example is my "annual" alyssum. As you can see from the stem, it's no young plant. It's certainly in its third, and possibly fourth year. The antirrhinums in the first photo are the same, and are covered with buds. They're going to give far longer, stronger stems of flowers this year than they ever have before.
I did cover the alyssum in the coldest parts of the year, as I also did for the marigolds and the surfinias. The marigolds eventually gave up, so maybe they really are annuals, but the surfinias certainly aren't. This year I was misled by a mild spell back in February, uncovered them, and lost them when the temperature suddenly dropped overnight. But last year, the overwintered surfinias from the previous year flowered all summer.
Obviously the temperatures here aren't that cold. It rarely drops below about -2° or -3° centigrade, and the balcony provides a sheltered environment where the plants can snuggle against the walls of the house for warmth. But the antirrhinums were uncovered on the edge of the balcony all winter, and were even snowed on with no detrimental effects at all.
Another plant which I'd always seen described on seed packets as an annual (now why would seed producers want you to believe plants are annuals when they're not , I wonder?) is Mirabilis jalapa. So when mine died down over the winter, I didn't think twice about it. But being too lazy to go out and throw it away in the cold, it stayed there till about six weeks ago. And when I emptied the containers I found thick tuberous roots. Not the usual sign of an annual. So I stuck them back in the pot to see what would happen. And lo and behold .....