Can the credit card company keep the chargeback open until you get the refund?
No! The Issuer cannot reopen the chargeback request after many, many months.
Many credit cards seem to be currently rejecting chargeback if the airline replies that it will provide refund (whatever the timing).
This is fraud in my eyes. If the Issuer backs down, the merchant (Thai) has won and (most likely) will never issue a cash refund.