With an Earth/Lava bender, a Fire bender, a group of Air benders, 3 Earth/Metal benders, and an Avatar, the chances of survival should be pretty high. I'd expect at least a few bumps and bruises among the non-benders, but nothing more than that.
Kuvira is a boss. She was using Junior from the start and I really don't believe she ever loved him. Why wait until after the conquest of nations to marry? She was merely dangling a carrot in front of him to make him do her bidding. I guess poor Junior has no choice but to go back to his family now.