The end-game would have included a chase at speeds far beyond the speed of light (because fuck physics); the Milano chasing down the massive crystaline ghost 'vessel' to the edge of the universe, before it entered 'dark space' and maybe created another Big Bang (or maybe not); space/time would have blurred, allowing a fight, but with a place to pause for the characters to decide whether to attempt to 'kill' the ghost, reason with it, or just let it go.

Naturally, the ending would have depended on what our heroes chose, and if they came to blows with each other due to disagreement.

Someone would have been shot in the Real World, giving that character a taste of how the mundane deal with such things, and the reality of no hope of meta/super help.

After finding the Space Gem in the Real World, we would have hit Star Wars just in time to be captured by an Imperial Remnant in the Milano. Luke Skywalker would have come to the rescue, assisting in finding (and defeating) herald of Galactus the Silver Surfer, attempting to locate the Time Gem so his master may trade it to Thanos, though for what reason we would not have known. A fight with a cloned Darth Maul would have gone down, resulting in the maiming of one our party.

Our group would have sprung onto the Gotham City scene just in time to assist Batman in fighting his rogue's gallery. (Condiment King, anyone?) Batman would have helped our heroes figure out Thanos' end game, and taken our band to Zatana--in order to magically "call" Dream, of the Endless. Dream would have been able to explain that cosmic forces beyond the Endless had "stolen" Marvel's Death when Death of the Endless went missing, afraid of another Blackest Night, figuring the Marvel U could handle it on their end.

Of course, at the end, Batman would have told us all to "Get out of my city, and never come back." During this, Jean would have been forced into the Joker's head, and not to her benefit.

Steve would have recognized Bucky in the suit, and slyly/silently given a nod of approval. Our characters would have taken on a Hydra unit during the height of the Battle of the Bulge. The Red Skull would have in his possession another Infinity Gem, and once taken by our team, would have instantly 'zapped' us to the Virginia countryside...

...and right into the sights of Daryl and Michonne, from The Walking Dead. The pair would have lead us back to Alexandria, and a surprisingly casual meeting with Death of the Endless, unable to get home on her own. After a brush up with the Wolves and an immense horde, someone in the group would have been bitten, causing a choice to be made by the group. Death leads us back to the DCU, and a confrontation between Death of the MCU and Death of the DCU.

This would've lead to a return of Death, and a thankful Thanos would have revealed the location of the great crystalline ghost, the big bad. Then the chase, and the end game.