Well, unless the copyright holder of that code decide to use another licence in the future — then the snapshot that was licensed as GPL will remain available to

Well, unless the copyright holder of that code decide to use another licence in the future — then the snapshot that was licensed as GPL will remain available to you, but the main strand of development may not. But yes, if this copyright is spread over many people (as it is in this case), then re-licensing is a herculean effort that is especially unlikely to succeed if it's designed to take away user rights, so in that sense a GPL'd project is more likely to remain open.