If you have completed the Ceremony of Eternal Bonding with another player then the emote, items, and mount you receive as part of the plan will still be available even should your partner choose to transfer to another World. The only feature that will not be accessible is the ability to teleport to your partner’s location. However, should the couple end up on the same World once more; the teleport feature will be again available for use.

Hope that answers your question!