Odds of Hanging On
The life span of a PR person is always up in the air. If you work for a company that's mundane and doesn't have a lot of public attention, you'll likely be okay. Your contact list will grow and the associations that you have made will make you more valuable to your company over time. Plus, it'll help you perform your job more efficiently, since you'll know who to call to get the help you need when problems occur.
However, keep in mind that usually all it takes is one project that went horribly wrong in the eyes of some big shot, one event that went too far over budget through no fault of yours, or one really bad publicity nightmare that got away from you and your group, to make the ax fall swiftly.