Why did Terezi even want Vriska back alive? Out of guilt? Because that just made things worse, why didn't Terezi bring someone else alive or try to prevent deaths of Nepeta, Equius, and Feferi?

It was out of guilt. She regretted killing Vriska throughout the three year trip and it destroyed he self confidence. After Game Over Terezi saw a way to right her wrongs and make things better by bringing Vriska back. She didn’t keep any of the others alive because they weren’t her fault, it wouldn’t be fair of her to change the actions of other people which is why she only changed what she did. And is it really worse anon? At least everyone is this timeline is alive.