Probably it's not that easy to replace Lisp for something else at Google, since it implements a relatively complex search engine core. Thus it's still used. I guess they WOULD be happy to replace it, since Lisp is otherwise not used much at Google, AFAIK. ITA/Google also developed another complex application using Lisp (a reservation system for airlines, initially for Air Canada), but that wasn't successful in the market.
At Viaweb Lisp was used for an early web store maker (enables people to have their own webshop) implementation.
> company gets acquired for its tech
Actually companies get bought for a business model, customers and some amount of tech. Reimplementing earlier approaches, even multiple times, even multiple times with different technologies, seems to be normal in the web business.