To start off with, the Compilation was never necessary. Sure, we had some questions. Primarily, did humanity get spared by Holy? But even that question, left unanswered, was a plot thread given emotion and impact to the original work because it wasn't given a clear answer.
The original game was good on its own. Everything with the Compilation has been expansion/exploration and making up new plot threads within those titles. Geostigma? Made for AC. Deepground? Made for DC. Genesis? Made initially for DC and then ultimately for CC. BC was very much an expansion of the pre-Barret AVALANCHE scenario and a reinterpretation of the Turks.
A sequel to end the Compilation is, in the same way, not strictly necessary. Yes, we wonder what Genesis is going to do. That's the only big question everybody has. In comparison only a handful are curious to see how the Seventh Heaven family develops, what Rufus Shinra's ultimate goals and dreams are, how the energy crisis of the FFVII world will continue to manifest (if at all) etc etc.
If one is not interested in getting more "for the sake of more/expansion/exploration" then a sequel to end the Compilation is not for you.
EDIT: I realize I avoided the question of whether or not Square "should" make a sequel. I guess my ultimate answer is that there is no "should" or "should not". If they are to pick a reason for a "should", then I'd want them to make this sequel out of solidarity to the fans of FFVII. But the reason will primarily be game industry economics, politics and random choices by board leaders and the strained relationship between those who want to mostly make money and those who want to (mostly) realize a creative vision.