According to one location, the change was due to corporate-side menu restructuring although they hope that Subway will introduce new items to replace the discontinued meats.
While roast beef and rotisserie-style chicken no longer appears on Subway's website menu and can't be ordered online, there's a chance that your local Subway may be going through whatever supply they have left of roast beef and/or rotisserie-style chicken and, if so, you can order them in-store.
Photo via Subway.