Exotics do not have a max power level and will never sunset.

Are they sunsetting exotics?

Destiny 2 Sunsetting: Exotics remain untouched

Some of our favorite Legendary weapons were retired, but fortunately, Exotic weapons were not subject to sunsetting. This means you can continue to use your favorite Exotic weapons in end-game content and challenging activities.

Is Bungie going to remove sunsetting?

In a new blog post, Destiny 2 developer Bungie has announced that sunsetting is being removed from Destiny 2. ... Players should expect some more significant balance tweaks from season to season now that sunsetting is gone, as Bungie wants to keep the game's metagame fresh.