Attempting to look up the answer to another problem, I found this.
I've always thought you could use a heal to restore decreased abilities, regardless. However, the REG says:
A heal ability can be used to remove the effects of a discard ability or an ability paired to a poison ability from a character.
This says that heal only works on abilities, not game rule (such as discard by the numbers.) It goes on to say:
A character healed from the effect(s) paired with a poison ability gains back any strength and toughness lost because of it.
Given that Gates of Samaria isn't a poison, one can't heal numbers from it?