This is a good idea. I think it should probably be generalized to any time the election status is changed. For example, we should probably also force a backup when they set cards printed. That's another critical backup they should make.
The only concern I have is the "nag" factor. If people are early in the election process, or just learning GEMS, then the forced save is going to be annoying. Its very important that they do these backups though. The only answer we can give people if they accidently un-set-for-election is to "restore from backup". If they haven't made the backup, they are currently SOL.