>In thirty years LaTEX will still be open source and probably will be maintained.
The latter is a genuine concern. Will it be maintained? I like LaTeX a lot, but would I want to maintain its internals? No. Could I? If I were paid handsomely, yes. Emphasis on handsomely.
Which leads to another worry: LaTeX itself may be OSS, but down the line it is possible that maintained forks will be controlled by big publishers paying maintainers to deal with the insanity of its internals. And we all know how lovely those publishers are (凸ಠ益ಠ)凸
TeX Live started in 1996, current update release is March, and has active conferences next year. They're an open source group, that has so far survived the test of time, and I'd suggest motivations are there to keep that into the distant future.
Unless academia collapses.
I hope you are correct!