Another ways to add rigidity to a damaged board is to add strips of PCB material oriented vertically across the board (ie. on their edges) and tack soldered. Obviously this will only work where there are large areas of copper, such as the cracked end of the OP's PCB and maybe in a couple of other places too.
The other thing is to prevent the crack from propagating further across the board. This can be achieved by drilling a clean round hole (around 3mm) just past the end of the crack, obviously avoiding any tracks. In the OP's images, the crack appears to stop at a solder pad, which might achieve the same thing, but it's hard to see clearly (the microscopic end of a crack may not be immediately visible).