The overflow to Ribblesdale has been hypothesised for some time. To my knowledge no-one's ever got any dye through. But anyone who has ever been inside the short cave at Austwick Beck Head will have realised just how immature the passage is and perhaps pondered on whether some of the water from the many magnificent Allotment potholes also goes somewhere else.
The regional dip is to the north east. The Sulber fault is in that direction from Juniper Gulf etc. It's understandable that the excess floodwater may then go along this fault, which passes relatively close to Blind Beck Cave. The latter suddenly produces a very significant flow in very wet conditions, consistent with it acting as an overflow for a major system.
All the above evidence is circumstantial of course - but you can see how it might easily be possible. An analogous situation occurs in the Peak Cavern system (Derbyshire). The normal flow in Speedwell Cavern drains to Russet Well and Slop Moll. In flood it overflows via Treasury Chamber (and other routes) so the excess water then comes out to daylight via Peak Cavern, a completely different underground route. Another example (nearer home in the Dales) is Sleets Gill, where normal flow drains to Moss Beck and floodwater overflows via the main cave entrance, which is a considerable distance away. Underground "distributaries" are't particularly uncommon.