20-Year Prospect
Language is constantly evolving and changing, as is this career. Lately, linguists have taken to working with computer languages as well as in computer-human interaction.
While it's unlikely that we'll be done translating ancient texts any time soon, there will always be new sorts of linguistic work that pops up.
With booms expected in the translation industry, the tech biz, and neuroscience, linguistics is as safe a bet as any. That is, if you're betting against the lizard takeover.