I have one constantly connected to an ethernet adapter because my MBP's wifi cuts out randomly throughout the day (which kills all my remote sessions of course).
This helps only with laggy connections with the occasional lost packet. Not with hard network drops (not to mention, there is more than just the terminal impacted by hard network drops).
No, mosh doesn't work like that. You can turn off the network connection in one of the nodes (both the server and the client) for hours and when they come back you still have your session like it was before the connection dropped.
I do this everyday on the client side (taking my laptop to work, opening the lid and having my session going on), and sometime on the server side as well.