I do expect that it will taper off eventually and then drop for a bit before leveling out (not being pessimistic, it's just a simple fact that much of the current growth of Lemmy, or for that matter kbin or other reddit alternatives, is due to people leaving reddit, and eventually everyone that wants to leave who is willing to consider this place will have come over, so the growth will stop or at least revert to a more "normal" pace, and not everyone will end up liking Lemmy, and so there will be some fraction of people that don't stay long once the hype over people moving from reddit has died down). However, it should still stabilize somewhere much higher than things were before the migration, so my hope is that it gets enough momentum that the number of people that remain when this incident is over is enough to sustain a functional community.