When is the last time an OSS programming language that took off actually died? For example, even though it's not as popular Perl 5 is still used professionally in many environments and as far as I know the ecosystem actually went through a sort of renaissance a few years back.
And these days I think it's even easier for OSS ecosystems to achieve critical mass and sustain themselves for decades since communication is easier (a lot more broadband internet in the world) and there's a lot more programmers around. Python, Ruby, PHP & co will probably be around long after I'm dead.