D&D 5E Would you play or run a game if the party's members are not the protagonists?

[Saeviomagy]

I had this idea for a campaign once where the PCs would be sent to be the companions on a heroes journey. They would meet up with the young displaced farmboy, travel with him, make sure that he appropriately fulfilled the prophecy for the one who would face up to the evil overlord... but be absolutely sure that he never became competent. Their job would be to make sure that he defeated the appropriate enemies, won the appropriate wars, completed the appropriate quests, got the appropriate magical doohickeys, but when he reaches the final confrontation with the evil overlord, he will still be a milksop farmboy and he will get slaughtered. Prophecy fulfilled, evil overlord set to rule for eternity.

Anyway, the answer is that your players should always be driving the story. If at any time you find yourself designing a scenario that your players do not participate in (and by participate, it could be that they influence how it turns out, or they merely try to survive it), then you've probably made a crap adventure.

 

[Eltab]

I was thinking of running an adventure where you are supporting the "heroes", maybe the party is just part of an army and they have to scout out act as spies. The core concept of this is that there are bigger things happening around and characters can't deal with that but they can help.

"Rise of Tiamat" can play with this theme.
You can do scenes where the Council is giving other Adventurer Groups missions. Low-level hero groups can ask the (mid-level) Heroes for help because they got in over their head. The PCs are sent on a research mission then have to deal with the mess they uncover. Eventually the PCs should be the heavy hitters who High Command turns to when they need a hard job done.

Build up the reputation of an NPC who is high in the chain of command early on, eventually the PCs get brought into his inner circle.

 

[Ezequielramone]

"Rise of Tiamat" can play with this theme.
You can do scenes where the Council is giving other Adventurer Groups missions. Low-level hero groups can ask the (mid-level) Heroes for help because they got in over their head. The PCs are sent on a research mission then have to deal with the mess they uncover. Eventually the PCs should be the heavy hitters who High Command turns to when they need a hard job done.

Build up the reputation of an NPC who is high in the chain of command early on, eventually the PCs get brought into his inner circle.

I believe D&D Encounters/Adventure League could work*, right?

I have no idea what DDAL is all about.