Coal:
From other coal mine BK's i have seen, the buying party negotiates with land lease holder to either assume the existing lease or structure a new one. Mineral leases are a little different from other land leases, as the miner is obligated to pay some level of royalties to the land owner. If i remember, the land owners has a market royalty rate of 6-8%.
A sale of Gwenco would leave Quest with no assets, at least that I know of, my guess is a reciever would be brought in, close up the books and file for revocation of the stock listing. then shut off the lights.