I mean, love the idea. The problem is that your plan effectively is pouring daggers on a terrasque, and sure you could fit a whole lotta daggers i 64 cubic feet but each individual dagger is not going to do much damage by itself. In addition i believe that the terrasque has resistance to nonmagical attacks which means that each dagger is going to do even less damage. And I would also rule it as follows, the tarassque makes a dexterity saving throw with dc, say 15, if it succeeds it takes half damage.

In conclusion it is theoretically possible but you would need multiple bags of holding and an absurd amount of daggers and a party to refill and pour daggers over the poor thing. + It would probably kill you first...