gimp-plugin-export-layers is a GIMP plug-in that exports layers as
separate images. Features include:

 * Export in any file format provided by GIMP and any installed
   third-party plug-ins
 * Treat layer groups as folders
 * Preview layers to be exported
 * Customize export with additional operations and constraints

See the plugin from "File --> Export Layers..." with another option
of "File --> Export Layers (repeat)" to subsequently export the same
image (perhaps reworked) with identical export settings. Comprehensive
'Help' is available from within the plugin.