What would happen if Linus Torvalds were to stop working on Linux?
Linux development would continue. This is because (1) there are many other well qualified people who would be enthusiastic about taking his place and (2) the full source code is always freely available to everyone, including to all potential successors to Torvalds. Fortunately, however, Torvalds has no intention of relinquishing his role as the chief developer of the Linux kernel.