The transformation of Loki into a star would shatter Thor's world. Thor has always had Loki in his life, whether as an adversary or an ally. This new form of Loki would be a constant reminder of what he has lost. Thor may become more isolated, feeling that no one truly understands his pain. He might also become more reckless in his fight against the enemies, as he has less to lose now that Loki is gone in such a strange and permanent way.
The star could symbolize Loki's ultimate freedom. Throughout his life, he was trapped by his own desires, by the expectations of others, and by his family dynamics. As a star, he is free from all that. It also might be a symbol of Loki's connection to the cosmos on a deeper level. He was always a bit otherworldly, and this transformation cements his place in the grand scheme of the universe. For Thor, the star could be a reminder of the enigma that was Loki, and that there was always more to his brother than met the eye.
I'm not sure about the exact title, but there are some fanfics where Loki turns into a star as a form of self - sacrifice. In these stories, Loki makes the ultimate sacrifice to save his realm or the people he cares about. It's a very poignant concept and makes for some really engaging reading.
One possible theme could be transformation. Loki going from a physical being to a star represents a huge change, not just physically but also in terms of his existence and how he is perceived. It could also be a theme of self - discovery. As he becomes a star, he may learn new things about himself and his place in the universe.
If Loki survived in Infinity War fanfiction, it could have led to a very different outcome. He might have used his trickery to deceive Thanos in some way. Maybe he could have pretended to be on Thanos' side while actually working against him. This would have added an extra layer of intrigue to the story as the other characters would have been unsure of his true motives.
One way to 'fix' the situation in a fanfiction could be to have Loki's faked death in Thor: The Dark World be more thoroughly investigated by Thor. If Thor had been more suspicious and dug deeper, he might have uncovered Loki's real plan earlier. This could have led to them working together more effectively against Thanos in Infinity War, preventing some of the tragedies that occurred.
Perhaps Loki would find a way to bring back some of the fallen. With his magic, which is often underestimated, he could search for ways to reverse the effects of the Infinity Stones. This would be a huge task, but if he managed to do it, it would change the course of the entire universe. He might start with trying to bring back his brother Thor, as their relationship has always been complex yet deep.
If Loki survived Infinity War, it might have opened up new storylines and character developments. He could have played a crucial role in finding a way to reverse the damage or caused more chaos.