Better prepare your template for accidental purges 
I solved this problem by adding a super small group to my templates that is locked for editing and assigned to a ‘hidden’ tag. In that group I have placed lines/faces that are assigned to tags that I absolutely want to save/keep. If you ‘accidentally’ hit ‘purge’ when saving, those tags will still be there.
image: hidden tag with the group size 1x2x5 cm (not visible even when i forget to hide the hidden tag
)