Let's assume they shrink from 300 to 30 employees. After some time they adjust internal processes, focus on the original goals and main use cases, weeding out unnecessary features, and having stable applications for Desktop, web & mobile. 30 people should be sufficient to maintain & support & maybe even improve it a bit for a long time given a healthy revenue stream from loyal customers.

Not sure if something like this ever happened in the history of software. :)