It's the same with all software, really: to be able to do a large scale project you have to have funding from somewhere, as you need developers full time working on it to fix/write the stuff no-one wants to fix/write. Some OSS projects get this funding indirectly by sponsored developers who work at company X and write OSS code all day for the project (this is what Linux uses). Other projects are funded by VC money, licenses, support contracts or ads. It's not common a large scale OSS project is successful and stays successful without any funding from the outside.

Thus, if a piece of software gets its funding by selling licenses (like with Hyperdex Warp), it's the same as with a company getting funding by sponsoring: if the cashflow stops, the show ends. In the case of OSS you can grab the sourcecode at least, but in the end, to successfully maintain that it takes a lot of effort most of the time, as the projects are often large, complex and the internals unknown to the user.