Honest answer: the company that purchased the plant and other assets is private today and has no reason to purchase the shares/company and take on the $80M debt. That would be really really dumb on their part.
The debt ridden empty shell has a market cap of what , 1.5 million . No assets, no employees and no board of directors to even make a fantasy deal . There is nothing left but a slow death in fantasyland.
With BioAmber the secured creditors are impaired - so they will vote on the POR.
But the unsecured creditors - preferred and common shareholders won't get to vote because the Court assumes since they will be wiped out they will vote against the plan.
It would be illegal for the secured creditors to be impaired but the common shares would remain intact.
That is why you will see thousands of posts saying the "shares are safe" - but not once have they provided any proof - all they have is pinkyland wishful thinking.
So the answer to your question is that there won't be any shares to buyback - and no company to buy them back.