You should always direct people to a landing page where they can choose from or be directed to multiple different instances.
https://kbin.pub/en or https://kbin.fediverse.observer/list
https://join-lemmy.org/ or https://lemmy.fediverse.observer/list
You can direct people away from specific instances if, for example, they have been de-federated.
The question is, are they generating enough content without that external source that it wasn’t felt much? If that’s the case, then it shouldn’t matter. If it isn’t, then people will leave and go to where the content is. Frankly speaking, my thought is that the federation should only be on as a backfill or last resort- if you’re unable to generate content and discussion organically, import someone else’s discussion.