Well, there ARE at least a few things that are unique to the iPad that left me deciding to keep mine (beyond the fact that I'd get virtually nothing in trade on an almost 5-year-old iPad Pro).
First, there's the ability to use the iPad with an Apple Pencil to take notes and draw freehand.
Second, there's the whole tablet thing--there ARE times when it's simply nicer to hold a tablet instead of a screen and hinged keyboard. With respect to the latter, I'm currently using my 12.9 inch iPad Pro as a screen on which to watch media, including iFit videos, while exercising on my exercise bike. There's no way a laptop would be stable resting on the stand that sits atop the handlebars on the bike.
Bottom line, while there IS a fair amount of redundancy inherent in having both a 13 inch MBA and a similarly sized iPad Pro, there are also some uniquely different functions that might well justify keeping both.