20-Year Prospect
Look around you. Things are only getting more techy, and boy, they were pretty techy already. This can't be the first time you've heard this: software is changing (and will continue to change) everything. And no, Mr./Ms./Mx. Sketch Artist, you and your job are not immune from its advances.
The police are using composite software instead of sketch work more and more often, while sketch artists are being forced to hyper-specialize or expand their skill set to remain gainfully employed. Portraiture and caricature work might still be safe from those dastardly computers a few decades from now, but when's the last time you heard of a street artist donating his posthumous multi-billion fortune to charity?
What's the world going to look like in twenty years? We don't know for sure, but probably not this. Stick with the times and you'll probably be able to find work, but it'll be harder for sure.