Thanks for the detailed suggestion, that's a mistake I've made myself! It's in for the next update (1.0.11): Settings → "Ask before not blocking at all". It's off by default, as you suggested. When it's on and you're about to move past declare blockers without assigning any blocker while you have creatures that could block, NeoForge asks first, with "Back to blocking" highlighted and "Continue without blocking" next to it. If you have nothing that can block, it stays out of your way.