When the LLC that had been taxed as a partnership only had one member, that partnership was terminated. The partnership would have to file a final return as of the date that there was not more than one member.
As a single member LLC that entity is taxed as a disregarded entity. For an individual member that would be on Schedule C for services or selling goods.
An S corporation can be a member of an LLC. An S corporation that is a single member would report the activity as part of the S corporation return. This is treated as a branch or division of the corporation.
So, the S corporation can acquire the LLC membership from the shareholder either with a purchase or with a contribution from to capital by the shareholder.
Once the membership interest is transferred the LLC activity will be part of the S corporation tax return.
Since the corporation and the individual are distinct persons it is not proper to have the corporation report the LLC activity until it is the owner of the membership interest.
As for 2012, it may be necessary to consult an attorney in the client location to determine if such a purchase or transfer is valid under state law for a date in the past. My layman understanding is that, in general, such purchase or transfer can not be post dated or be effective for a past date.
Please ask if you need more discussion or clarification.