I don't understand. If they hire a maintainer, are they going to pay the maintainer or the maintainer must get enough donations/sponsors to support the salary and also pay a fee?

Also, once a project is in the project, how difficult is to go away? Is it necessary to assign the name or the repo of the project to this association?

I think the project has to have the funding already via donations or sponsoring - they state they can employ people "If your project has a sufficient amount of funding".