Asking anyone to outright state the future of technology is simply bad faith business - especially as we have no idea exactly what your project entails.
The product is supported until next year, after which you're on your own. If your project is a simple 2D app that has minimal dependencies, it's probably going to be okay, barring some fundamental web architecture changing, which is often highlighted well in advance.
Having used C2/3 for almost a (oh God) decade, the engine very rarely actually breaks - it's often specific feature on a specific platform - depending on what this is, you could refactor your project to work around it.
I would say your best bet would be to port your project to C3 - there's a whole community of us that would be happy to help, and you've got roughly a year in which to do it.
More information could help here - if it's a kiosk style bit of software, you could fairly easily simply lock the hardware to a specific browser and never update it - plenty of museums have done this with Flash based projects, and Director before that.