I've been thinking for quite a while, Since Usopp is not yet in the crew he may leave the enternal log to Elubaf behind for Luffy and the others to find with an note saying "Luffy, I'm in Elubaf. If you want me back in the crew, come and find me there"
Usopp left Water 7 with Karsee and Oimn to Elubaf with Luffy and others still in Water 7, looks like they have to go to Elubaf to find Usopp. What do you guys think? I had an feeling that it might happen