Many wild, seed packet bananas exist, but all (as far as I know?) bananas that we eat have no seeds and are actually all clones. Thus they are all under the extinction by disease threat.
Someone could in theory continually keep developing new strains of bananas in case of future diseases. Practically however there is no profit in that. You could argue a charity or NGO should do stuff like this.
Note that the Gros Michel isn't extinct. It's still grown as a boutique item. But the blight is apparently persistent in fields, and thus it can't be grown in quanitity without huge risk to the plantation.
