Endgame is now consistently losing badly to Infinity on a day to day domestic comparison at the same points of their run. The last few days its been 800,000 to 1,000,000 behind per day. Infinity only made 34 million more in the rest of its entire run so given current trends Endgame may only make 20-25 million more domestically. That would put it around 840 million domestic and would put it between 2.733 and 2.738 billion worldwide meaning it would need make 50 million worldwide to beat Avatar. If its falling off overseas the way it is stateside it may not make it but will be within 34 million which is what Avatar made in its brief re-expansion. Its going to funny watching many pout using it as an excuse if this happens while ignoring that Avatar's money was in 2009 dollars meaning that on a ticket to ticket basis Endgame is going to be well behind Avatar.
That said if it gets really close I can see Disney pulling some hijinks, like a special edition with some bonus content, to nudge Endgame past Avatar much like someone did to nudge Black Panther over 700 million when it had been stuck at 699 million for well over a month with no chance of closing the gap until suddenly on its last weekend of release it went from making $400 a day nationwide to making tens of thousands a day.