Xerostomia is a common side effect of radiation. It is more or less , depending on the area treated.
In some cases nowadays we can spare the salivary glands to some degree and it is not AS bad. Sometimes , if IMRT is used , it can decrease the dose and some recovery occurs over time. If 2 dimensional or even 3D was used and it is a tongue lesion then recovery would be minimal. Many people adapt to it with time.