Well, Doctor Strange 2 takes cues from multiple related comics, combining and adapting different plot points and characters to create a unique cinematic experience. It doesn't have a one-to-one correspondence with any particular comic issue or series.
Doctor Strange 2 is not directly based on a specific existing comic. It takes inspiration from various Doctor Strange storylines and elements from the Marvel Comics universe.
Yes, there are similarities. The basic character traits and powers are often retained, but there are some creative changes for the cinematic adaptation.
If Doctor Strange comic had a different ending, it might have altered the perception of the characters and their development. It could have also impacted the overall theme and message of the comic. Maybe it would have opened up new plotlines and possibilities for future stories.