If you have exceeded the VAT registration threshold then you *must* either:
1) Apply for VAT registration; or
2) Apply for exception for registration.
(2) will apply only where you can satisfy HMRC that your income over the next 12 months will be below the deregistration threshold (Â£59k).
I have had success in the past with applications for exception from registration that have not had any physical evidence to back them up but each case will be looked at independantly by HMRC.
On the basis that you have absolutely nothing to lose, I would recommend that you write to HMRC applying for exception and stating that your partner's income will fall below the deregistration threshold as he is to take some time off. It will help if you can state exactly what he is likely to do with this time and, if he is not earning, how he will support himself.
Senior VAT Consultant