Well, what would an MBT be replaced with? You'll still need a vehicle carrying heavy weapons to take out bunkers, enemy vehicles, etc. Maybe you can have an ATGM carrier with a bunch of missiles. But missiles are expensive, so maybe if you fit a specialized fire control system to a gun you can get the same accuracy as a missile but cheaper. That's going to be heavy, so you'll probably want tracks to spread the weight[0]. Then you'll want to protect your big and heavy vehicle too so it can't be killed by say someone with a common RPG-7. And now what do you have? A tank.

Certainly things are going to change in the future. Active protection systems (APSs) are going to be basically required, and I wouldn't be surprised if APSs became the main armor. After WWII the effectiveness of HEAT made designers believe armor was ineffective, so many post-war designs sacrificed armor for speed, such as the Leopard 1, so something similar could happen again.

But an important part of the equation is tactics. A very similar question to "why do we still need MBTs" is "why do we still need infantry" and the answer is the same: they synergise[1]. Infantry need tanks to blow up hard points, and tanks need infantry to keep an eye on the surroundings, suppress and occupy potential firing points, take buildings to prevent them from being used to fire ATGMs and to use to look out for enemy ATGMs, etc. Infantry itself doesn't do anything to reduce the threat of missiles, but infantry-tank coordination tactics do.

[0] For example, the Stryker MGS is a wheeled vehicle carrying a gun. It's widely regarded to suck badly, but in principle there's no reason you couldn't have a good wheeled gun carrier.

[1] Also you need infantry to go places tanks can't go and root out defenders, plus actually do the work of holding enemy territory like talking to local leaders, clearing the radio station of hostile DJs, etc