If the memory was not available, an exception of type std::bad_alloc would be thrown, and your handler would begin executing instead of the code that attempts to use the bad pointer. Or, if you don't have such handler, the program would be immediately terminated.
No, that check is useless: if allocation succeeds, sPtr is not null and the condition in the if is never true. If allocation fails, the exception is thrown and the if() is never executed.
What exactly would you like to prevent? How do you plan to handle the out of memory condition other than by terminating the program?