It is less work and cost to have a single license server. Having 7 license servers or the like is a higher cost. You don't need dedicated servers though. You should be able to use an existing server for this.
But then you have to weigh in what happens if the connection between the offices goes down. If you have the file server centrally it is an indication that you would be fine with a single license server. Or can the users continue work if the connection between offices is down, and how often might it happen? Just some thoughts to consider.
Jimmy Bergmark
JTB World
http://www.jtbworld.com
JTB FlexReport - network license and software usage reports
http://www.jtbworld.com/jtbflexreport/index.htm
Jimmy Bergmark
JTB World - Software development and consulting for CAD and license usage reports
https://jtbworld.com