Thats how we all learned to incremental save. Zbrush seriously needs to put in an autobackup feature what with all the random crashing and mesh explosions that can hapen.
Anyway what works well for me and some of my coleagues is making 3 incremental save files, ex: 01 02 03 , then keep saving over the next one when you finish a general area, going 1,2,3,1,2,3,1,2,3. Dont do it too often because sometimes you do something bad and dont realize it till 1 hour later. the reason we cycle over 3 files is to save disk space from having a pile of increment files per object.