Earlier quoted context omitted.
How could GPL software disappear?
future versions / developments could disappear (or be licensed as closed source). I imagine that is what is meant.
The fact that the core team can stop development is a much more concrete problem. I wouldn't worry about it though, it's too valuable for too many people. Percona is patching MySQL, along with Google, Facebook, Monty's MariaDB company, etc. If anything, MySQL is more alive than ever before.