Scheduling articles will remove them from the Editing queue. They'll still be available e.g. in the Archives list or via the "Future Issues" interface, and you can still polish off any outstanding editing tasks. Typically, scheduling an article against a particular issue is one of the last steps prior to publishing -- if you're concerned about items disappearing from the editing queue, delay scheduling until you're ready to publish.
Open Journal Systems Team
Don't miss the First International PKP Scholarly Publishing Conference
July 11 - 13, 2007, Vancouver, BC, Canada