If you want, by all means continue to sign, but don’t hold your little guy back. Instead embrace the new milestone. You wouldn’t want your guy to continue crawling instead of working on walking, so it’s not justifiable to inhibit talking either. I know it’s sad in a way to watch your baby grow, but you’ll make many more memories as you shift into the verbal world.
So when you baby starts babbling, babble back. When they start saying their first words, get just as excited and make just as big a deal as you did when your baby added signs. Now is not the time to think about your own needs, think of what’s best for your baby. If you still want to continue to sign, there’s nothing saying you can’t. In fact, it’s to your advantage to continue to sign. Signing as your baby becomes verbal will help clarify words and reinforce them. As words become clearer, their signs will drop, but if it’s a habit you continue to do, then your baby will continue to do them too.