Don't you need the firewood to provide heat for all the people freezing to death? Using Greek fire for something like that is a waste of resources IMO.
Which runs out a lot faster than Greek fire. Not to mention, you don't know how long the ice will remain. It could be a few months, a year, one hundred years
In India we are using elephants, rhinos and man power to remove the rest of the ice by slowly making it collapse and and transport the ice rocks into the sea