I only still own one book of the trilogy, but IIRC:
• Destroying both sides is not implied to be possible.
• Team evil is sufficiently bat-**** evil that a win by team good looks to be preferable to a win by team evil, even to those who die. There is such a thing as a fate worse than death.
• The readers on not told anything about this ficton's afterlife, but the fires might well know.
• The death toll from destroying the earth is not specified. Despite your use of quote marks, "killing all the people" is your words, not mine. I didn't rule out survivors, and neither does the trilogy.
The information in the trilogy is consistent with the destroying the earth being good. Since the fires are consistently portrayed as good, it follows that, in this trilogy, destroying the earth is good, or at least consistent with being good.