You should consider grandfathering prior licensees and/or allow for a inactive status where you can continue to carry the P.E. title, but be non-practicing.  If you decide to become active again, you must make up all accumulated mandatory continuing education since date of inactivity in order to re-activate your license.  This is a similar process to the Real Estate Industry.  You never lose your license that you worked hard for, however, if you want to practice again, you just need to make up the CE time.  We worked very hard to obtain the PE license.  It should remain for life and not be required to take even more time investment.

Ideally, this is not imposed, but if it must be, you should allow for people who have obtained the title of PE to always maintain it in their signatures.  I currently work in the Computer Industry in Product Development Marketing and while I am not practicing, carrying the title increases my credibility with the engineers I work with every day.  It is an important title that enhances my working relationship with the engineering community even if I am not a practicing engineer.