I think Tonks and Remus would have both lived if it had only been one of them at the battle of Hogwarts. Since it's implied they died together it probably had a lot to do with them worrying over each other and that Teddy was at home and needed at least one of his parents to live. But then, I don't think only one of them going would be possible because the other wouldn't be able to stand being at home while their loved one was fighting in the biggest battle of the war.
Remus is a tragic character, making Tonks one by association.
He had to die, as much as it pains me to say that.
I can’t imagine the end being as powerful if he had lived. Him living to a ripe, old age just doesn’t make sense for some reason.
He and Tonks had to die, really.
Because neither would want to be apart from each other, but being together was probably what ended them.