delete does not free memory recursively, so if a dynamically allocated structure holds the only pointer to some allocated memory and that structure is deleted, the other allocated memory is neither released nor is it accessible anymore, so it becomes leaked.
In other words, yes. As you suspect, the int pointed to by sss[4]->x is leaked after line 11.
Yes. A class is identical to a struct in every way, save one: the default access specifier. In a struct, the default is public, and in a class, it's private.