It is just a partial result and explorative study at this point. I will go deeper.

But I asked the question, what happens when Bitcoin becomes the monetary standard?
Would an economy survive with a fixed money supply or to go a death spiral?
Many economists say it will go to a death spiral.
The answer is no, it doesn't necessarily.
Even in this simple toy model (not agent based but done this by solving differential equations) shows stable solutions.
I will share more result as I make the model more realistic.
Key Results (50-year simulation):
Growth & Deflation Equilibrium:
Real GDP grows 232% (≈2.1% annually)
Prices fall 36% (≈-0.8% deflation annually)
Velocity increases 108% (≈1.3% annually)
What's Happening:
Secular Deflation: With fixed M and growing Y, prices must fall to maintain M·V = P·Y
Velocity Compensation: Instead of a death spiral, velocity RISES to partially offset deflation - people transact faster as the economy grows
Stable Growth: GDP grows at ~2.1% despite deflation (slightly below the natural 3% rate due to deflationary drag)
Phase Portrait: The Y vs P trajectory shows the economy moving toward higher output and lower prices - a stable equilibrium path
Economic Insights:
Deflation ≠ Collapse: Mild, predictable deflation (-0.8%/year) coexists with healthy growth (2.1%/year)
Velocity is Flexible: V adjusts to accommodate growth, acting as a "pressure valve".
No Monetary Policy Needed: The system self-stabilizes through velocity adjustment