There is still enough time before the next euros and before then many things must have happened to this Spanish team. Moreover it is not always easy to win an international tournament back to back. Before that time some of the players at their peak now might have lose form and won't be at their best performance by then. The more realistic competition for Spain to win now is the world cup and I believe that's where they have set their sights right now. The world cup is closer than the next euros. This present Spanish squad looks likely to be playing together till the world cup, but I'm not sure they they will be together till the next euros. I can vouch for Spain to win the world cup than winning the next euros. I'm not saying it is impossible for them to do it, but in my assessment it won't be possible.
The Spanish squad is very young. They're filled with 17 to 23 year olds. If you look at the squad, you'll see there are already just as good replacements for the older players. The likes of Rodri have players like Casado ready to replace them. They would have struggled with a 9 to replace Morata, but now they have Samu who is equally as good even though he's young.
The next Euro is in 4 years and in 4 years players like Yamal, Nico, Casado, Pedri, Gavi, and Cubarsi, will be at their peak. They also have wingers like Zaragoza who is on loan from Bayern at Osasuna.
Saying the World Cup is easier to win for Spain is just false. The World Cup is a more difficult tournament than the Euros. The World Cup consists of other countries. Don't forget that teams like Argentina, Colombia, and Uruguay will also be at the World Cup. A country like S. Korea knocked out Germany in the World Cup. Don't also forget that the World Cup consist of the 12 best European teams, so they will meet tougher opponents at the World Cup and that makes it more difficult to win.