So long as it's their software they can change the license of new versions as they desire. If they decide to change the license and you depend on the software, you can maintain a fork of the project. I'm sure you don't like that answer, but this is exactly why open source licenses offer no warranty or promise of support, and you willingly decided to rely on some software with such a license. You can't just pretend like this aspect of the license doesn't exist because it's inconvenient for you.
If you want guaranteed support for any software, hire someone, or do it yourself!
I think a lot of the controversy surrounding these situations is that people aren't educated about what open/free software really is, or the ideals behind it, or don't care and just want free stuff from other people.
The idea is that you can use source code, modify it and create derived works from it if you desire (normally with attribution or whatever), and with the GPL there is an additional restriction that derived works must also be GPL'd. Free software does not imply that people want to work for you for free and doesn't imply that they intend on supporting the project at all.