In fact, if the process executes well, the ranking will not drain and even improve significantly. If it isn't, all your efforts will be wasted. Sounds scary? No, you shouldn't. Website redesign/development with SEO in the mindset with a firm foundation boosts your current SEO. Old URLs need should map to the new ones, and the quality of the content needs to improve or at least must retain.
No matter you have exercised SEO or not, there is some ultimate SEO checklist that you might want to know before going a redevelopment process. Go find out at the infographic, guaranteed you won't regret it by spending your valuable minutes looking at it.
Infographic by: digitrio.com.sg