Ask HN: Losing anchor client. Scared. What now?

I'm a freelancer who's been doing automation coding for the last few years. Just found out that my anchor client (who makes up >90% of total revenue) isn't going to renew me for next year. I'm the geek behind the keyboard, and don't know how to sell. I didn't have to sell to get the gig in the first place, because I was in the right place at the right time.