Yes the damage has already been done. Rin isn't the sole reason why Obito is doing all this; heck it isn't even one of the reasons at all. Rin's Death was saddening and the switch. The real reason was the fact that Kakashi broke the promise; he saw people everywhere dying; the world was full of pain; their was no hope or peace. These are the reasons to why Obito changed. Rin's Death simply flicked the switch on. If Rin was brought back to life (presumably by Rinne Tensei) Obito wouldn't care - Rin doesn't matter to him. [
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] All he cares about is completing the Moon's Eye Plan. If he wanted to bring back Rin he could have [
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][
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]. Rin no longer is any importance to Obito so no, if she was revived, it wouldn't change him.