the abuse of the well of eternity wasn't a night elf decision. it was Azshara (who's ancestors are the blood elves) who abused it's energies to open a portal for sargeras under the pretense that he would grant her more power, that and she wanted to jump his bones. it was Sargeras that possessed Medivh at conception to open the dark portal. it was Ner'zhul who corrupted Arthas and Kel'Thuzad, and it was Archimonde who made Ner'zhul into the lich king.
if the Titans wouldn't have had a "lets wait and see" approach to Sargeras's growing corruption then the only problem Azeroth would be facing would be the old gods, and Nefarian from cata. the orcs would still be living in huts in Draenor, the Tauren might very well have been friendly with the night elves and the alliance. the forsaken wouldn't exist, the blood elves would still be in the alliance, and the trolls would still be wholesale slaughtered... because honestly who really likes trolls?