I've no idea what would happen if a blackbird tried to swallow as wasp. On a couple of occasions I've seen frogs swallow wasps that have landed on the pond surface for a drink. On both of those occasions the frog looked a bit pensive as the wasp went down its digestive tract but neither frog made any attempt to spit it out, or appeared to suffer any visible ill effects. They just settled back with their eyes level with the water surface and waited for something else edible to cross their field of vision.
The blackbird hesitated for a few seconds - maybe that warning colouration really does work - and during that time the wasp managed to struggle free and got away. So I still don't know what would happen next if a blackbird swallows a wasp.
For another potential life-and-death encounter with an unresolved outcome click here