Throughout the MCU’s Phase Four and Phase Five, fans have gotten well-acquainted with the multiverse: the concept that there exists an infinite number of universes, with some appearing vastly different from the one we know, while others only differ a small amount. Various forms of Kang have been depicted as masters of the multiverse, capable of traversing it, bending it to their will, and working together to take out anyone against them, regardless of the timeline they call home. This is why he and his variants have been positioned as the Thanos-level (Josh Brolin) threats of the Multiverse Saga, which encompasses Phases Four, Five, and Six.
It’s also worth pointing out that the first “Avengers” movie post-“Avengers: Endgame” is titled “Avengers: The Kang Dynasty,” making it even more abundantly clear that Kang is baked into the future of the MCU. Though the folks at Marvel Studios likely could find a way to write Kang out of the franchise in favor of another overarching villain, it wouldn’t be the right move. Fans know about the Jonathan Majors situation, and fans remember how hard Kang was publicly pushed as the MCU’s next big bad. All of that information would loom large over an abruptly Kang-free MCU, likely to the detriment of the franchise.
Therefore, since the character is so essential to the MCU’s immediate future, there’s really only one viable way forward: recast Kang.