Most perennial plants will come back the same size or larger each year. A few plants that are not well-adapted to your climate/soil/etc. will come back smaller and smaller until they disappear. Some plants will reseed and you will get loads of little baby plants, and the original plant may die completely.

Depending on what you are growing and how cold the winter is. Are they pots or planters? Where are they kept now? When you grow in containers that are left outside, you expose the roots to freezing temperatures. Even if the plant puts on leaves during winter, you can't tell if you lost the plant until the spring when the pots thaw and see if the roots support the new growth or if it dies back. I have lost many plants this way. What are you growing? Some plants that I've had make a real cold winter in containers are chives and rosa rugosa and shasta daisies.

For us a complicating factor is very poor draining, almost pure red clay soil. Some winters it can get so waterlogged that perennials partially rot and come back smaller for a season, then recover and grow again until the next wet winter. So there can be quite a bit of variability. I harsh winters things may disappear altogether but may leave seedling from buried stems, etc a short distance away. RJ