When removing a product's option type, remove its variants' associated option values

app/models/spree/product_decorator.rb

@@ -1,4 +1,10 @@
 Spree::Product.class_eval do
+  # We have an after_destroy callback on Spree::ProductOptionType. However, if we
+  # don't specify dependent => destroy on this association, it is not called. See:
+  # https://github.com/rails/rails/issues/7618
+  has_many :option_types, :through => :product_option_types, :dependent => :destroy
+
+
   belongs_to :supplier, :class_name => 'Enterprise'
 
   has_many :product_distributions, :dependent => :destroy

app/models/spree/product_option_type_decorator.rb

@@ -0,0 +1,10 @@
+Spree::ProductOptionType.class_eval do
+  after_destroy :remove_option_values
+
+  def remove_option_values
+    self.product.variants_including_master.each do |variant|
+      option_values = variant.option_values.where(option_type_id: self.option_type)
+      variant.option_values.destroy *option_values
+    end
+  end
+end