I don't think there is anything to be concerned about.
Sublinks will live alongside Lemmy, just like kbin does today. Some Lemmy instances might switch to it under the hood at some point, but as a user you probably woudn't even notice the change. All the data would be preserved, so your community would still be there unchanged.
It is basically Lemmy written in a different programming language, with more focus on moderation tools afaik. So for users it looks and works just like any other Lemmy instance does, and it's part of the same Threadi-/Fediverse.