I'm currently using the Yahoo YUI javascript library in a couple of my projects.
However, I'm a little concerned about three things. First, they laid off 10% of their employees. Second, their stock price keeps falling: especially after ignoring the MS takeover earlier this year. Third, what if someone does buy them?
The only reason I bring this up is that I tend to build applications that are going to be around for 8 to 10 years.
What would you do?
Yahoo is a major company that won't end in the next couple of year.
The Yahoo! library is open source so you will have other people to continue to improve it IF Yahoo would go bankrupt.
No technology is 100% safe for 10 years perspective, I think you aren't in danger with it.
In 10 years Javascript will be completely difference and most framework will not be the same so I think whatever you choose you will need to change a lot of thing in 10 years ;) Just be sure to keep a version of the code in you repository to always have the latest version that work for your system and you will be fine.