Hmm that I am not 100% on. The IBJJF has gotten better about answering stuff in English, so you can email the
[email protected] and ask. That's probably the most direct way.
What I'd specifically say is that your instructor is not currently available to sign your black belt certificate application form, although he has previously signed your membership card. As a current member, do you need another signature to apply for the certificate? And if a 2+ degree signature is needed, can it be someone other than your instructor who previously signed?
These situations come up and there's always a way to solve it provided everything is legit. So I'd just ask and see what they say.
By the way the issue that I mentioned previously about how you would likely have to register under your new team next year is on the site: "15. If I have changed my academy, do I need to renew my membership?
If you are an athlete who is required to have a membership and you have changed academies, you will need to renew your membership under the new academy and have your new professor sign the membership form to confirm the changes. Once you have renewed under the new academy, you will be able to start registering for tournaments under the new academy."