It's been three days now and the danios are still alive and have actually ventured from the surface and are allowed to exist without visible threat in the middle depths of the tank, an area usually dominated by the tiger barbs. The barbs don't seem interested in them anymore. They either don't recognize them as a threat or taking up too much of their turf or they are tired of chasing and not nipping the fins of a much faster and more agile fish.
As far as options go for more fish for the tiger barb tank I'm open to suggestions but I have considered a few fish. A large, mature red-tailed shark might be mean enough and sizeable against a large school of tiger barbs. I am also considering tinfoil barbs; maybe a trio twice the size of the largest tiger barb would be a large enough presence to keep the cowardly bullies at bay. A trio of clown loaches might also be worth looking into but these fish are not as hardy as most fish and might still endure the same treatment the smaller rainbow shark endured. Some aggressive cichlids might be feasible if it weren't for the water chemistry being different. Bala sharks Of course another alternative is to simply get more barbs, specifically albino tiger barbs and green tiger barbs.