Will 'Internet Recovery' necessarily erase my hard drive?
No, doing an Internet Recovery will not erase your hard drive (unless you explicitly choose do to that using Disk Utility). It will only reinstall the OS for you. You should get your drive checked to see if it's just data corruption or a deeper hardware issue that has resulted in the question mark folder icon being shown.

Also, this question has been answered on superuser - see "Does Internet Recovery erase everything on my Mac?"