Argentina will survive without Messi. They have good depth in player pool. But I can't say whether they will be able to defend the trophy in 2026 without Messi
Argentina will continue to exist without Messi just like they continued their national team existence without Maradona many years after his retirement. Many players were considered as new Maradona but only Messi came closely to Maradona or we can say he is already bigger than Maradona?
Next few years, after Messi announce his retirement, we will see more young players considered as new Messi, Messi Jr. This will put more pressure on those youth players and not only few of them can grow up their career well. Maybe only one player will surpass Messi but will it happen soon or we will have to wait like 50 or 100 more years to see such player?
They have a very well balanced team with youngsters like Julián Álvarez, Nicolás González, Alexis Mac Allister and Enzo Fernández providing enough support to veteran players like Ángel Di María, Rodrigo De Paul and Messi. France also have a similar setup, but then the ci-ordination between different payers is not that great. Argentina on the other hand has excellent team cohesion.
Only Julian and Enzo are young enough to have good fitness in World Cup 2026. Allister is not old but three more years can change many things for a football player and he is not too young like Julian and Enzo.
Argentina always have many football talents but they might have some years with crisis like Brazil now. A good team have to play well without star and super star players because firstly they might not have such players and they can suddenly miss those players by injuries.