Add more nails to my heart - watching even younger versions of our beloved cast and knowing what is going to happen to them in the end. Sigh... what a depressing ending. haha

It pains me to even watch them all riding together at the end of episode 01x10 because you knows going to happen to them and even when you rewatch the series, you are defenseless. 

Merlin (or Uther, if he's the one to go back) would probably try to change things for the better.

Uther would be an interesting one in that scenario, if he went back to Morgana's childhood, maybe just after Gorlois died, and could start from scratch with her.

This would be indeed very interesting. However, changing the past would also mean that countless lives would be affected by it, people would be born who weren't meant to be born and in case that either Merlin or Uther went back in time to change things for the better, both actually wouldn't be able to travel back in time because once they change things, the reasons for them to make a time travel would disappear and they would have never travelled back and therefore never changed things... actually. :-D

It's always a paradoxon to make a time travel and to change things.

Nevertheless, if this is overlooked I'd love to see such a thing.

One option would be that, as the time traveller makes more and more changes to the timeline, they remember less and less of the original timeline. Eventually, they would reach a point where they would effectively merge with their other self and carry on, with no memory of any other timeline, so the challenge would be to set the ball rolling for a happy future before they forgot everything. It could be similar to Merlin Sickness.

I personally think everything would have been different if this we're the case. I personally believe that it was not an enchantment that drove Morgana over the edge, but numerous crimes towards her commited by the other characters. In particular I think Merlin poisoning her was what truly drove her over the edge. Merlin was the only person she could truly confide in about her powers, the only person she had left that she could trust, and when he poisoned her, that trust was shattered.

If Morgana knew from the Mark of Nimueh that Merlin had magic, I do not think she would tell Uther as she has from the very first episode questioned Uther's policy on magic. Instead I think she would bide her time and whilst she is torn between loyalties to Uther and what she deems to be right, she would see the good Merlin does for Arthur and likely decide not to say anything.

When Morgana begins to see images of the future, she would likely confide in Merlin who would be much more straight with her, and likely work with her to save Arthur from Aulfric and Sophia.

After saving Mordred together, I expect that they would be in complete trust of each other, Morgana would see through him and Mordred the good of magic where as Merlin would have someone just like him to talk to and confide in.

With this, as Morgana begins to understand the extent of her powers, Merlin would comfort her and stand at her side, as her loyal friend and confidante.

With such a close friend and someone who really understands her in Camelot, I do not expect she would so easily go towards Alvarr's side, after all given the close bond between the two it is possible Merlin would share his destiny with her, and therefore she would better understand that Alvarr is a problem for Camelot. Also, she would not need him as much as she did as she would not be alone with Merlin around.

With Merlin as her close confidante, it is once again unlikely she would fall so closely in league with Morgause and without Merlin to poison her, it is unlikely she would partake in her plan.

Overall I feel like things would continue as they were for Arthur, with Merlin and Morgana at his side, Uther would remain king for much longer (as Morgana would not be around drive him insane, aide in his murder etc.) and Camelot would flourish, with Arthur eventually becoming king and leading Camelot into the Golden Age we have all heard of with Gwen, Merlin and Morgana at his sides.

I never really understood why Merlin didn't just tell Morgana he had magic as well... it might have kept her from feeling so isolated and allowed her to see that she could use it as Merlin did, to protect the kingdom.

Am I missing something here?

In The Tears of Uther Pendragon II and The Sword in the Stone II, we still see that there was still a hint of the good old Morgana, behind that evilness, that Merlin and Arthur were able to bring out of her respectively. If she was able to fully trust Merlin without knowing about his powers, I could not even imagine how strong their bond would have become if she knew.

This reminds me of Gilli who Merlin showed him his powers to let him know he understands how it feels, but did not do so with Morgana. She has a good sense of humor, at that, and I could imagine her laughing with Merlin behind Arthur's back while Merlin plays pranks on him, and learning something from Merlin, like speaking telepathically to one another in the castle, letting Gwen in on their secrets, not to mention Gaius, and I could imagine Arthur and/or Uther being concerned that the two have affections for one another.

She believed in Arthur at the beginning, even though in her own grief she did not confide in him also, but in Merlin, who she also goes to his home to aid in the battle of Ealdor despite her status in Camelot. Although, I cannot imagine better episodes for Merlin to reveal his magic to her other than The Mark of Nimueh and The Nightmare Begins.

Then again, she was seeing Merlin in her dreams in Le Morte d'Arthur and she never even wondered why that was so...

AND FUNNY... There is this hidden place that she likes to pull Merlin into so they could whisper, both before she is evil and after she turns evil. Now let your imaginations drift... She could be pulling Emrys into that place to do something else... if you know what I mean!!!

Morgana would still hate Merlin/Emrys. How could she not? Merlin betrayed magical people by helping not one but two tyrannical murderers (Uther and Arthur) massacre them. 

Moreover, Merlin helped Arthur to steal Morganas birthright.