I forgot to add a half tsp of salt to my oat & maple scones! What are the chances that they won't turn out edible?

If you discover this before baking, you could sprinkle with a little salt, like a pretzel, or brush with a salty glaze. Sounds like you've baked them, so in the end maybe it was better to find out that less salt was OK!

Still delish!

I think they'll be fine! Maybe lacking a bit of extra flavor kick, but definitely edible.