If Avengers Infinity Wars taught us anything it’s that you CANNOT expect to know how the plot will span—and this is just as true for the people working on that series as it is for the fans.
Did you ever expect that Thanos will have all the 6 infinity stones in the third installment? Or, for that matter, did you expect half of the superheroes dying? Poor Peter Parker :’(
A lot what we saw on Avengers Infinity Wars, no one expected it. And even the actors working on the movie revealed that they didn’t know about the plot either. Many of them were made to shot additional scenes to ensure they never know the entire story. They were never told about the plot.
And, above all, they were made to sign some clauses that prevented them to disclose any information about the movie. (Although I am not sure about this; it could be just the rumors).
The ending of Avengers Infinity Wars had multiple versions. And it’s likely that only the Russo Brothers and a very close knitted group knew the real plot.

(Courtesy: Comic Book)
It’s quite fascinating to think that they maintained such secrecy around a movie—even the actors never knew the story. To think we have so many leaks on military and political secrets around the world courtesy of Wikileaks and more—and never did we know the story of Avengers Infinity Wars until its actual release.

(Courtesy: Screen Geek)
Coming to your question, it’s not surprising that Avengers 4 has two endings right now. In fact, there are well reasons to believe that it could be plenty. There could be plenty of versions of the story to trick the people working on the sets, including the actors—much like it happened in Avengers Infinity Wars.

(Courtesy: Indy100)
Nobody knows what will happen in Avengers 4. Who will die? Who will come back to life? Will there be some news on Hawkeye? How will Captain Marvel come into the frame? What kind of farewell will Steve and Tony receive? Cab we see Thanos vs. Hulk duel? These are questions with no answers until we get to late April 26.
Let’s just hold our breaths and wait. Personally, I have never been this excited for any movie ever. :D