Not really, because the very people who will be telling them this is an 'onboarding instance, we eventually want you to choose another instance and move there', will also be the ones telling them all about the possible instances the new comers can move to.

Maybe its a bit like an orientation at a university. They are specifically not the same as the courses students will eventually attend, the orientation (onboarding instance) has a different purpose to the course (home instance). You may meet people you'll never see again, the guides role isn't to be the course lecturers/administrators (analogous in this case to mods/admins) that you'll interact with throughout your course.

There might be a little passing sadness if you get to the end of orientation if you've had a very enjoyable experience, but the student (user) has expected the end, they've known when and why its coming. And hopefully if they've enjoyed the experience on the onboarding instance that much, they are that much more excited for the next steps.