IDEs can open classes by name, wherever they are on the classpath. I'd normally have all projects open in any case even on quite large codebases - it's very practical with modern hardware.

Indeed, but it takes some time to get there in case of dozens or hundreds of modules in different git repos (again, depending on the size of your ecosystem).

I just don't see how this is a problem. For any class on your classpath, ctrl-shift-t or whatever will go to it. If removing a dependency lead to missing that class, you can probably just open it, and you can certainly revert the removal and then just open it. Or do a classname search on your internal maven repository.