Current financial issues aside I'm not sure how such a launch system could work in the longterm. The whole business seems to be built around a feature which I'm pretty sure is unique to the 747. Production of that plane stopped several months ago which has consequences for spare parts and qualified pilots. In the meantime rocket engines will only get more efficient and we'll start to see boosters which can be flown to any location across the globe, either as cargo or under their own propulsion (ala Starship P2P).

When Virgin Orbit was spun off, Virgin Atlantic was still operating a dozen Boeing 747-400s. Perhaps before they were phased out early because of COVID the plan was to retire those to Virgin Orbit or use them for replacement parts?