Skip Demuth asks about the replacement process. http://app.leg.wa.gov/RCW/default.aspx?cite=42.12.070 which involves selection of qualified individuals to serve until the next scheduled election.
I always prefer to see the people of Langley choose qualified candidates to represent them on the Council -- directly through free and open elections.  
If she chooses not to run again, Rene Neff is doing the people a service by making her intentions known early, and allowing potential candidates to consider a run in plenty of time to file with the County Auditor. I strongly suggest that she consider timing her actual decision so as to make a choice or her successor (and likely safe incumbent in the next election) by the remaining four members of the Council unnecessary. 
In any case, thank you Rene for your service.