We just finished simple interface to safely request transfer of your shares to Bitfunder:
https://coinbr.com/btct/idiff_1Transfer will be possible until 2 weeks before asset expiry (October 9 for CB.IDIFF-E, November 6 for CB.IDIFF-O). If you hold both -E and -O you need to fill it twice.
If you don't take any action here, untransferred IDIFF contracts will be paid out in due course as per the prospectus. Payouts will be sent directly to your bitcoin public address(not via BTCT). So you lose nothing, only trading of your shares will not be possible.