Annuals come and annuals go. There are cool season annuals for winter. There are warm season annuals for summer. Really though, there are all sorts of annuals that are not annuals at all. Most are some sort of perennial that has the potential to last longer than a single season. Only a few popular ‘annuals’ would necessarily die after blooming and producing seed, within a single year.
To be clear, true annuals last only a single year. They probably germinate from seed early in spring, and grow quickly. They then bloom in spring or at least by summer, and subsequently produce seed. Once their seed has matured and been dispersed, their job is done. They finally die in late autumn or winter. Annuals from deserts are even faster because of the harshness of the weather.
Many large-flowered sunflowers are true annuals. They are finished once their seeds mature. They will not bloom again. Even if they wanted to, they would not survive through winter. Petunias should be annuals, because they also die over winter. However, it is possible for them to survive winter in a semi-dormant state, and regenerate and bloom again the following spring and summer.
Realistically, it is not practical to salvage petunias for a second year. It is easier and more efficient to plant new ones. Yet, it sometimes happens, particularly in mixed plantings where old plants can get cut back while cool season annuals dominate in winter. Alternatively, lanky old stems can get buried with only their tips exposed. These tips might grow as new plants the following spring.
Cyclamen are cool season annuals that have been dieing back for summer. They usually get removed by now. However, in mixed plantings, some of their fat tubers can survive through summer to regenerate next autumn. For what they cost, they are worth salvaging! Primrose, chrysanthemum, impatiens and the various fibrous begonias are all worth salvaging through their off seasons.
Fibrous begonias may not know what their off season is. Those that bloomed through winter might be looking tired by now. If pruned back, they could regenerate as warm season annuals. Those planted in spring might look tired by the end of summer. If pruned back early enough in autumn, and protected from frost, they might grow enough before winter to work as cool season annuals. Cutting them back and waiting for regeneration may not be much more effort than replacing old plants with new ones, and is less expensive.