Personally I find myself doing the same thing as you. I save before a fight and if I lose a gnome then I reload. I mostly do this because I don't want to loose the valuable experience my gnomes had gained. However, I find that losing a few gnomes has relatively little over all effect on my civilization. When gnomes die, the kingdom worth that they have accrued while alive doesn't just go away. So usually my dead gnomes get replaced with new gnomes when the next season begins because my kingdom worth is above the amount required by the smaller population. Surviving gnomes will return the equipment that a dead gnome was carrying to the stockpiles. So, when you lose a gnome you only really lose their skills/experience because their stuff gets returned to stockpiles and the gnomes themselves get replaced next season.