pH stops falling once the bacteria stop producing lactic acid. Yes, in cheddar, and most other cheeses, some bacteria continue eating the lactose, but decreasingly so. Usually, it will stabilize 1-2 days after press, and then over time most cheeses will rise a little in pH during maturity. Some, like emmenthaler, rise a lot, all the way to the high 5s or low 6s.
You are right, vac sealing does inhibit the natural interactions, but not so much of the bacteria, which enter an anerobic/survival phase anyway, but more so of the physical cheese. Oxygen, for example, aids some catabolytic and proteolytic processes. Similar to wine in analogy, but different pathways.
You will produce different flavors when you vac seal vs air age.
And yes, the bacteria first eat, then slow down eating as they run out of food, then go to sleep, then slowly die off over time.