they killed off iron man because he was too expensive and his character was becoming too integral to the MCU as a whole
Captain America they wiped off because I think Evans wanted out
The plan was Dr.Strange and T'Challa to be the new leaders. that would've been strong but you know what happened
so now we just have Dr.Strange and no other character to share the load
contenders are Reed and maybe professor X. Spider-man will always be an ally to heros as long as Sony plays nice will be around too.
Captain Marvel is supposed to be part of the trinity but well she can't even get her name billing in the sequel
whoever is black panther will not be the leader of the avengers unless it's t'cholla's son from the future or a t'challa variant
imo Stark and Cap are coming back for the IW/EG event 7-10 years from now
Old man Stark and Cap from another universe then they bow out again