Yes, it will equilibrate to whatever volume of CO2 is soluble in water at whatever given temperature you have your keg stored at.
It would be the same as opening up a two liter and closing it back up again. Gas will come out of solution to re-pressurize the headspace until it reaches equilibrium. So maybe the first time you vent (depending on headspace), your keg may repressurize itself to 52psi after a while. Then you vent again and it repressurizes to maybe 48psi or whatever will fill the headspace.
It won't stay carbonated at the same level unless it's held at the same pressure/temperature.