Who else would have could have stopped Lord Voldemort and his Death Eaters, had Harry Potter died in the Forbidden Forest?
A number of people would have continued to defy the Dark Lord and lead the rebellion, but it would probably have been a new Trio who would have coalesced in the persons of Ginny Weasley, Luna Lovegood and Neville Longbottom.
You know Voldemort's snake, Neville? He's got a huge snake.... Calls it Nagini ..."
"I've heard, yeah.... What about it?"
"It's got to be killed. Ron and Hermione know that, but just in case they-"...
..."Kill the snake?"
"Kill the snake," Harry repeated.
Harry Potter and the Deathly Hallows - J.K. Rowling
I kind of think that if Harry had gone beyond the Veil it would have taken all of the air out of Ron and Hermione. They were just so closely tied to Harry, it was like they shared the same magical shield.
They were technically not as strong as Harry anyway (if we're going to call Lily's magical blood protection a strength) so they wouldn't have been able to withstand Voldemort and they would have been next in line for the Nagini-guillotine if Harry had been taken out.
Even between the two of them, it would have been more of a Romeo and Juliet type of ending, not going down without a fight, but going down nonetheless. But there were other members of Dumbledore's Army and the ones that come to mind immediately are Neville, Luna and Ginny. Neville and Ginny kept the DA going during that last year under Snape as the Hogwarts Headmaster.
Neville is kind of a no-brainer; anyone who knows the Harry Potter story well understands he had more anger towards Voldemort and the Death Eaters than anyone but Harry, so he would have had more motivation than anyone. He had also grown into a strong wizard by the Battle of Hogwarts, so there was no lacking in ability.
But he couldn't have done it alone.
If we look past whether we think Ginny and Harry were a good pair or not, Ginny was still a gifted witch who grew up with a house full of gifted wizard-brothers, two of them being named Fred and George Weasley.
"The thing about growing up with Fred and George," said Ginny... "is that you sort of start thinking anything's possible if you've got enough nerve." (Ginny to Harry when he wanted to go behind Umbridge's back to talk to Sirius Black)
Harry Potter and the Order of the Phoenix - J.K. Rowling
The Weasley twins taught Ginny that anything one can think of, one can pull off. And Ginny would have been filled with an unstoppable fury if Harry had really died. She kind of fell apart when she thought he was dead, but that would have been a very short-lived response,
think.
And Voldemort would have completely overlooked her as a threat, considering he never even recognized her as someone of emotional value to Harry.
So Ginny would have done anything to defeat Voldemort and that would have included just staying alive until the job was done, our match-making opinions aside. She loved Harry that much and she was just very smart and able, too.
Luna would probably have taken over the reins as brains of the operation, kind of a more open-minded, structure-free version of Hermione. Assuming losing Harry also included Hermione and Ron, that would have been four deaths of people close to her that would have brought forth a determination in Luna to finally rid the wizarding world of its greatest evil.
...the beak of the eagle opened,.....a soft musical voice said, "Which came first, the phoenix or the flame?"...
"...I think the answer is that a circle has no beginning." (Luna to the brass eagle to access the Ravenclaw Common Room)
Harry Potter and the Deathly Hallows - J.K. Rowling
Was there anyone left in the Wizarding World that could’ve stopped Voldemort and his army if Harry decided to move on at King’s Cross Station?