What happens if this plugin stops working?

First of all, you should be aware that any open-source software maintained by an unpaid individual can stop functioning any time soon. This is why I'm trying to avoid introducing plugin-dependent stuff into PDF++.

Note

Supporting the development financially is a great way of increasing the chance of the project continuing to be maintained.

That said, all of your links to PDFs will keep functioning even if PDF++ is dead. This is because PDF++ does not introduce any original syntaxes except for &color=<COLOR NAME>, which is completely optional.