I agree that sidebar incorporation may be on a decline, and that off canvas menus can also accomplish the job. However, I have had use cases where having a sidebar proved to be helpful.
For instance, I noticed a couple of examples having a vertical menu/sidebar while browsing the forum to see sites made with Blocs. One of them was http://www.camertonholdings.com/companies.html (which I found here: NEW! Camerton Holdings Website)
The site has a sidebar (on the left), but it doesn’t scroll down with the rest of the website content (on the right).
I’m sure there are workarounds to working with such a design, but having the option for an affixed sidebar will definitely prove to be helpful.
Additionally, the link I had shared with the sidebar on the right is Bootstrap’s official website, and is responsive. However, if you’re referring to the sidebar menu being responsive, it just hides itself on a non-desktop interface. Even then, I feel that such a sidebar is good for navigating and providing the user with situational awareness when a user has lots of screen real estate i.e. on a desktop.
Would love to hear your thoughts! (And hopefully have this feature as well!)