I can’t speak to what happens everywhere else, because I do all my racing in the midwest. I’ve raced with KART in the past, when CES held joint events, and, from my perspective, were a joy to race with.
To the point, however, when it comes to my part of the country, what has hurt the sustainability of road racing is a lack of interaction between the local tracks/clubs and the regional road racing. So, my answer to the question posed is no, road racing cannot survive without the clubs. Karters, almost invariably, start at the sprint level (as they should) and then get introduced to road racing at some point, hopefully. If there’s no interaction between the clubs and road racing, there’s no one to replace the inevitable drop outs when karters retire, have kids, get divorced, lose employment, etc.
The national series that comes through my neck of the woods has certainly done nothing to foster growth in participation, and, arguably, has actually harmed it. I’ll stick with having a regional series run by people who actually know what karters in my region want