We all now know that in the new timeline, Sarkhan was never born. However, Doug and Maro have both stated repeatedly that the changes to history will be confined to Tarkir and won't affect the multiverse at large. Doug specifically mentioned that "somebody who called himself Sarkhan" appeared on Alara and Zendikar and fulfilled the same roles in those storylines. [http://dougbeyermtg.tumblr.com/post/109109557374/people-seem-convinced-that-the-reforged-chain] Are we ever going to get a fuller explanation for that paradox?
Furthermore, how exactly was Sarkhan able to travel through time in the first place? The hedron shard he was carrying somehow reacted with Ugin's grave and created a portal through time. But, um ... why? At no point have we been told that Ugin or the hedrons have time powers. Even if they did, why would they react that way? Did Ugin purposefully intend for this to happen in case he died?
Xantcha, Phyrexian Reject
Jodah, Archmage Eternal
Tovolar, Howlpack Alpha
Pivlic, Orzhov Informant
Crixizix, Master Engineer
Feather, Boros Peacekeeper
Marisi Coilbreaker
O-Kagachi
Gix, Phyrexian Praetor
Karn, Father of Machines
Yawgmoth, Father of Machines
Serra, Mother of All Angels
Tevesh Szat, Doom of Fools
Leshrac the Nightwalker
Jeska, the Thrice-Touched
Elspeth Returned
Crucius the Mad
Taysir the Infinite
Urza's Head (Unglued!)
Furthermore, how exactly what Sarkhan able to travel through time in the first place?
I'm thinking this will just get swept under the rug. In general we don't know anything the characters don't and people at Wizards clearly see time travel as a dangerous plot device. They don't want to event hint at time travel happening again in the foreseeable future.
Furthermore, how exactly was Sarkhan able to travel through time in the first place?
Simple explanation
The actions of Sarkhan in the past (Fate Reforged) disturbed the timeline. Since Ugin did not die in the past, his bones (Ugin's Nexus) in Khans or Tarkir are surrounded by a magical anomaly created by this disturbance in the past. It is the place in time and space (Nexus) where the fate of Tarkir was changed, so this is why it is a portal through time.
Also, Sarkhan hedron shard has nothing to do with time travel, it is only used as a search device to find Ugin and then to create the cocoon.
In Sorin's Revelation story, it is clearly stated that mortal cannot go in the Ugin's Nexus, only someone with a Planewalker Spark can approach it without being torn to shred.
"Take me down there. I must see for myself."
"It is dangerous," his guide said, emotionless. "All who enter the chasm have died."
"I don't care," Sorin said with a surge of ire. "Move. Now."
They reached the floor of the chasm. A section of skeletal tail could be seen jutting out from the snow, the bluish mist emanating from it. The closer they got to the bones, the more Sorin could feel the forces at work—powerful magic from another age.
These were Ugin's bones.
The warrior guide began to falter as he struggled forward.
"Stop," Sorin said. The warrior wobbled on his feet. "No need for you to get ripped to pieces. Move back."
The warrior turned and took shelter in the lee of a boulder as Sorin moved toward the ghostly arc of ribs that rose overhead. The closer he came to them, the more he could feel the tidal forces of magic as they pulled at the very fibers of his being. He could feel the spark within him respond, holding him together as he moved upward through the Spirit Dragon's ribs toward the skull
But then how come Sorin did not travel in time you ask? It's simple, he was not able to draw Disenchant with his Bitter Revelation, so he was unable to destroy Ugin's Nexus and gain the extra turn.
Furthermore, how exactly was Sarkhan able to travel through time in the first place? The hedron shard he was carrying somehow reacted with Ugin's grave and created a portal through time. But, um ... why? At no point have we been told that Ugin or the hedrons have time powers. Even if they did, why would they react that way? Did Ugin purposefully intend for this to happen in case he died?
Xantcha, Phyrexian Reject
Jodah, Archmage Eternal
Tovolar, Howlpack Alpha
Pivlic, Orzhov Informant
Crixizix, Master Engineer
Feather, Boros Peacekeeper
Marisi Coilbreaker
O-Kagachi
Gix, Phyrexian Praetor
Karn, Father of Machines
Yawgmoth, Father of Machines
Serra, Mother of All Angels
Tevesh Szat, Doom of Fools
Leshrac the Nightwalker
Jeska, the Thrice-Touched
Elspeth Returned
Crucius the Mad
Taysir the Infinite
Urza's Head (Unglued!)
Almost certainly. With Tarkir block winding down I'd expect it to take a while.
I'm thinking this will just get swept under the rug. In general we don't know anything the characters don't and people at Wizards clearly see time travel as a dangerous plot device. They don't want to event hint at time travel happening again in the foreseeable future.
Simple explanation
The actions of Sarkhan in the past (Fate Reforged) disturbed the timeline. Since Ugin did not die in the past, his bones (Ugin's Nexus) in Khans or Tarkir are surrounded by a magical anomaly created by this disturbance in the past. It is the place in time and space (Nexus) where the fate of Tarkir was changed, so this is why it is a portal through time.
Also, Sarkhan hedron shard has nothing to do with time travel, it is only used as a search device to find Ugin and then to create the cocoon.
In Sorin's Revelation story, it is clearly stated that mortal cannot go in the Ugin's Nexus, only someone with a Planewalker Spark can approach it without being torn to shred.
But then how come Sorin did not travel in time you ask? It's simple, he was not able to draw Disenchant with his Bitter Revelation, so he was unable to destroy Ugin's Nexus and gain the extra turn.