No, you should be able to weld that without putting enough heat in to melt the braze or affect the strength. The dropout is higher carbon steel, so I'd use MIG with CO2, because it'll be harder a harder weld than with argoshield. File it to a vee, weld it as a series of penetrating tacks letting it cool in between each, dress it back, job done. You could wrap a wet rag round the frame ends if you wanted to stop the heat getting into the braze, but I doubt you'd have to.