Automatically save the file before a subdivide processes. Create a userpref or modifier setting toggle for this option.

I would rather wait a few seconds more for my file to automatically save before a subdivide attempts to process than lose a bunch of sculpting work because the subdivide refuses to complete successfully due to lack of memory, which either causes Blender to hang unceasingly, or have both Blender and Windows crash either from a misclick or because of unpredictable behaviour.

This could be optionally toggled either in the user prefs menu or as an individual setting in the subdivision or multiresolution modifiers themselves (or a separate toggle that enables/disables such a toggle even appearing in the modifier's settings). It would be a nice stopgap measure before there is possibly a future implementation of a way to cancel/undo a processing subdivision.

Typically, more complex objects and or scenes will make such an autosave take longer, but again, I'd rather wait a bit than have hours of work lost because I didn't save the file myself, for which the current Autosave/backup feature does not actually save Edit Mode or Sculpt Mode changes.