Unfortunately, wildfire is an inevitable part of summer in the West. Sections of the PCT can and do close due to fire. In the event of a closure, the Pacific Crest Trail Association works with land management agencies to recommend detours around the closure.
Here’s the current, most up-to-date state of closures on the PCT. These are subject to constant change, so keep an eye on the website too for more info and divert your hike where necessary: