The Econ 101 demand-and-supply story serves to illustrate a simple point: Markets tend to move/adjust towards equilibrium. However, such adjustment is neither instantaneous nor perfect; rather, it takes time.
For simplicity, let's first imagine we have perishable goods that must be consumed by the end of each day. On Day 1, producers set the price too high at $P_2$ and there is excess supply AL. And so at the end of Day 1, producers end up with AL units of unsold (and wasted) goods.
On Day 2 then, producers will probably wisen up a little. They'll probably produce a little less and reduce the price by a little, so that excess supply is reduced by at least a little.
If on Day 2 there is still excess supply, then on Day 3 we'll see still further reductions in quantity produced and prices, and hence a still further reduction in excess supply.
This common-sense story tells us that over time, the market will tend to move towards equilibrium. However, this adjustment process is neither instantaneous nor perfect. It happens gradually, over time.
In the case of non-perishable goods, the adjustment process will likely even be slower, because, as you rightly point out, there is now the possibility that producers can store their inventories and sell today's unsold goods tomorrow. The $Q_2 - Q_1$ goods can indeed be stored and we can try to sell them tomorrow.
However, it is not free to store inventories. If every day producers produce $Q_2 = 1,000$ units but consumers buy only $Q_1 = 600$, then each day we'll add another $Q_2 - Q_1 = 400$ units to our inventories. Our inventories will keep piling up.
And so over time, even with the possibility of storing inventories, producers will recognize there is persistent excess supply, wisen up, and gradually reduce the quantity they produce and also their prices. Excess supply will thereby gradually be reduced.
The story is the same whether goods are perishable or non-perishable. The only difference here is that we'd expect a market for perishable goods to adjust more rapidly towards equilibrium.