Mergers...is is still possible?

[aopirose]

Would a merger between 2 NPCs even be possible today???

Almost anything is possible. It would depend on the purpose of the merger and how willing the parties are to achieve that purpose. For example, is it to pool resources but under a new name? AOII merges with ABC to become QRS.

What would happen to the Alumnae? Would they have to be initiated into the other sorority?

Usually, alumnae are given the option of initiating or not.