Avengers: Endgame - Everything That Changes If The Heroes Steal The Infinity Stones From The Past

4. No Guardians Of The Galaxy, Xandar Survives

The whole plot of the first Guardians Of The Galaxy ended up being about an Infinity Stone (and indeed, the film was where we got to know about the history of the Stones for the first time from The Collector), so you remove the Stone and you remove the film from the MCU.

If the Orb is taken from Morag before Peter Quill gets to it, he can't meet Gamora who has her own agenda for the Orb and they (along with Rocket Raccoon and Groot) can't get arrested and can't meet Drax on the Kyln. The Guardians, thus, never form. More likely, Quill would have been pursued by Rocket and Groot throughout the galaxy on their bounty and that's about it.

Without the Guardians and the Orb, Ronan The Accuser's history would also change. He might have had a more free run at Xandar, but he'd lack the Power Stone to destroy it and the Nova Corps would probably thwart him. And that planet's later destruction would also have been averted since it would never become the resting place for the Stone after the Guardians defeated Ronan.