Probably the biggest challenge would be adhering to the:
- Vertical Side Menu
- Header Area Structure, with the right sidebar overlap
- Perceived 3 Column full height layout
But overall after a quick glance there does not appear to be anything otherwise that Blocs could not handle. By default it does not offer vertical menus currently, so you would need to work that out however you wish.
I would suggest try creating a page template and accomplish those 3 things mentioned above, along with the rest of the home page. If you can get those to your liking then the rest of the 110 (+/-) pages, look pretty standard otherwise at quick glance.
You could certainly recreate the site in Blocs, but the identical structure may not remain, and perhaps could even be improved upon in the revised rework process. I would take the opportunity if converting it, to maximize the UI/UX and improve it, where you can and would decide to. It’s a great time to reconsider and make such adjustments.
Blocs will help it be responsive also. But since it does not presently appear responsive you will need to make decisions on how the 3 columns collapse and stack in a logical fashion, again perhaps a good opportunity to rethink things overall with the site structure, etc.,
Hope something proves useful to you.