…as the title says - Maybe it was too much for poor Blender As soon as I clicked “Join selected meshes”, blender died and the recovery file was of an older ‘project’. What can I do so this doesn’t happen EVER again? Apart from saving often (I guess i did the scene so fast that blender didn’t get to autosave anything, long live dupliverts, lol)
Blender should save a file Quit.blend every time is closes or crashes, holding a snapshot of whatever you were last doing. Aside from that, to prevent such things, you should just be conscious of what you are doing (I always keep my eye on Task Manager or System Manager to watch RAM usage), and you should save often.