The output current required from the 3.3V regulator is
1uA * 0.999 + 50mA * 0.001 + 25uA = 75.999uA
The output power is
3.3V * 75.999uA = 250.8uW
The input power to the regulator is
250.8uW / 0.8 = 313.5uW
When the batteries are fully charged the input current to the regulator is
313.5uW / 3V = 104uA
If the batteries have a flat discharge curve then you will get a life of
2700mAh / 104uA = 25837hours = 2.95 years
Since your batteries are 2700mAh 1.5V AA I am guessing that the discharge curve is not flat. You will need need to draw higher currents as the voltage drops.
Also your regulator efficiency probably drops at lower voltages. Again I am guessing since I have not seen the design.
Be careful when calculating using currents. You may be inadvertently assuming that the input and output voltage of the regulator is the same. With an input of 3V and an output of 3.3V it is not a big error. If you do a more accurate estimate of the battery discharge curve it will matter.
(* jcl *)