I’m not sure of any of these are viable options, but here are my thoughts.
If hosting it does not cost you any money, I’d say don’t shut it all down. Just leave it as it is, with a note saying that you will no longer update it/provide any support for it, as well as a means for people to contact you in case they want to take over.
If hosting it costs you money, maybe try to find an alternative, free solution so that the project remains accessible? Again with an email where people can get in touch if they want to host it and continue working on the project themselves.