The simple version is “take away Challenges”. The MC can create Words on the fly. The party is fighting an Ogre? Great, “Ogre” is a Word with a cost of 3. The Ogre can’t be persuaded by the silver-tongued Bard? No problem, there’s a “Hostile” Feature worth 10 points. Good luck on that roll, Fflewddur Fflam. When the MC rules that you’ve done enough damage, the Ogre dies, or is converted to Calvinism, or whatever you were trying to do.
A basic assumption of Grand Adventure is “what I narrate will come to pass in some form”. There’s two factors keeping you from success all the time. First is the expendable nature of your Pool dice. You don’t get everything back to roll again. Instead, you only recover up to the star rating of the Action. The second is related to the first: to keep yourself running dry quickly, you’ll need to spend Twist dice reasonably often.
“Failure”, in this case, means an increasing reliance on Twist dice. Twist is where you get to say "you put an arrow in the ogre, but you stumble, fall, and hurt yourself." There’s no real equivalent of the PbtA 6 or less result here, where just everything goes to shit because the dice say so. I don’t have a clear idea how to do that with the game engine as it stands, and I’m not convinced it would benefit.
In short, that’s the problem you asked to have, if you give up using Challenges - I can’t advise you. But I can tell you roughly how fast characters will run out of dice.
TL;DR: if Challenge costs scale with PC advancements, a typical Action will probably cost between one-half and one die.
A verb-type Word usually costs a flat 4. This means on average it costs 1.6 dice to activate. You have a 50% chance of reaching 4 or better on 1d6, and better-than-50% odds of reaching it on 2d6 or more.
A modifier with a cost of 1 (Bravely, Sneakily, etc.) always costs 1d6, no matter what. The use case for modifiers at low levels is twofold: to get around repeated actions (“Confront Ogre”, then “Confront Ogre Bravely”, for example), and to give yourself a chance to reroll bad dice. What do I mean by that? Say you roll a 1 and a 3. The 3 is enough for your Ogre, but the 1 is awful. Bravely brings a third die into play from its Pool, and if that rolls a 4 or higher, you put the 1 on Bravely and the 4 on Confront.
Challenge Words have variable difficulties, but 3.5 points of activation cost is 1d6 on average. So a Challenge that has a cost of 7 activates on 2d6, on average.
You can recover dice based on the star rating. That means the average dice cost of an action is (1.6 + (Challenge Cost / 3.5) - Star Rating). For example, a 1-star Confront Ogre Action, with an Ogre rated at 3, will typically cost around 1.5 dice to use. That cost comes out of Pools, either a PC’s normal Pools or Twists.
Assuming starting PCs took a 1-die Twist every action, they’d run dry in four moves each. Every advancement will typically give them another Action: one more Pool die, plus either a new Word or a Level Up of an existing Word.