I worked for a company which went into administration whilst one of our owned aircraft was having a check with an outside maintenance provider. The engineers refused to release the aircraft until they were paid. After the administrator explained the situation to them, and having presumably sought legal advice, we got the aircraft back.
If an aircraft is leased, it isn't owned by the airline and the leasing company are perfectly entitled to demand its return if the agreed rate isn't being paid, however for any money already owed they stand in line with the rest of the creditors. Given the current situation, a new customer won't be immediately available and the leasing company will be responsible for storage and other expenses such as maintenance and insurance once they take it back. Therefore it might be better to wait and see for a few weeks, depending of course on the terms of the lease. The aircraft are multi million dollar assets and the owners will want to see that their investments are protected ie insurance coverage is kept current and maintenance carried out on schedule. The last thing they want is an aircraft written off whilst uninsured or its condition deteriorates whilst grounded necessitating expensive repairs.