I do wonder, did that happen to you? And what do you do when the new web designer is not a Mac user, and only uses Wordpress? What would that mean for the client I built the website for in the first place?
Yup, happened to me before.
My project file is mine and will not be handed over. The contract between me and the customer states that I own the project file, they own the published version of the site, and can do with that published site as they please, but have no rights to the project file.
Besides, the new dev would not only need to be a Mac user, but they would have to be familiar with RW+Stacks and own all the stacks and the frame work I used to build that site.
I do provide a zipped published version of the site for download in my self service portal and refer customers to that if they want to hand the site over to someone else, or if they wish to host it themselves instead of hosting it on my servers.
If they intend to hand it over to someone else, it’ll be up to the publisher to import that published site into whatever tools they use.