....Could've Hermione used the time turner to go back in time and stop Tom Riddle? (i don't know how far in time a time turner can go but if it could've gone 50 years back in time than....)
If not, it still probably wouldn't have ended well.
As Hermione herself says when she stops Harry from going into Hagrid's Hut to kill Peter Pettigrew (when the trio are still inside), "Bad things have happened to Wizards who meddled with time".