Oh no... I just had a thought at What could be a FFVIIR DLC...

Remember the ending? Zack being alive and dragging an unconscious Cloud? We know it's a Different Timeline and all that, but... What if, the Zack lives timeline becomes the FVIIR DLC?  think about it it would make sense in a Riku mode in Chain of Memories kind of way...

Of course this would mean that new dialogue would have to be recorded and that some sections wouldn't be exactly like the original. Many of the Sephiroth Visions would have to be cut out. Zack's motivation to work for Avalanche would be to get money for Cloud's treatment. Of course, with Tifa being there her motivations to fight in Avalanche are slightly different. She, like Zack would fight to protect Cloud. The first Encounter with Aerith would change to after the Sector 5 reactor explodes to have Zack fall into the Church twice. We get a happy Zack/Aerith reunion and the reason Zack is hellbent on going back to Sector 7 is his buddy, Cloud. Aerith is curious to meet this friend that Zack is willing to give everything for, because of "a feeling".

They encounter Tifa riding to Corneo as the normal story mandates. They Wall Market section would change after the Corneo arena with Zack knocking out Leslie and entering Corneo's mansion.

As the party heads into the sewers, the delirious Cloud, armed with a nail bat, finds his way out of Sector 7 into Sector 6. The plate falls as normal. The Party finds Cloud near the Honey Bee Inn and take him to Elmyra. With the party climbing to the upper city, Cloud escapes Elmyra's house and attempts to climb to the upper world, but gets captured by Shinra Security.
After noticing the Mako glow in Cloud's eyes, they contact HQ and Hojo takes interest in this "Mysterious SOLDIER".

The party infiltrates the Shin-Ra building as normal. After rescuing Aerith, they find Cloud convulsing next to the JENOVA container. The game follows the normal path with Zack fighting Rufus,  while Barret, Aerith, and Red XIII attempt to escape. Tifa stays with the delirious Cloud and Zack. Sephiroth reveals himself and talks about Cloud's role in changing Destiny. With Sephiroth defeated and not sure if their fight was worth it, the party leaves Midgar.
We get flashes of Zack's stand against Shin-Ra and Stamp is a beagle. Then we get Cloud screaming over Zack's corpse and grabbing the Buster sword. Zack, carrying Cloud and Aerith pass next to a Delirious Cloud painfully walking towards Midgar...

Or it's what I'd do if I had to do a Zack themed FDVIIR Gaiden.