MSP430 GPIO behaviour on power off
There are a few voltage levels you need to maintain.


VCC(Start) or V(Min), the lowest that clock operations can happen.
This is the voltage that the Power On Reset circuit operates at. It's
0.7 * V(B_IT-), typically 1 Volt. The MSP430 should be in POR reset at that time.
V(B_IT-), the Brown Out Reset circuit trigger voltage. Typically 1.35
Volts. Any quick drops below this voltage triggers the BOR reset.
V(B_IT+) or Vhys(B_IT-), the BOR circuit hysterics value. Minimum
voltage after power drops to the BOR trigger, in which the BOR timer
starts. It will be held in reset up to 2 milliseconds after it rises
past this. Typically 150mV above V(B_IT-). V(B_IT-) + Vhys(B_IT-)
should be ≤ 1.8V Max.
V(Min), the Minimum Operating Voltage. This is 1.8V. Anything below
this is undefined/bad. Between V(Min) and V(B_IT-), you have no idea
what is happening.
Vcc(MhzMin) for Your Clock speed. Not all clock speeds are supported at all VCC voltages. For example, 3.3V is the minimum for 16 mHz. If VCC drops below this, undefined/bad, again.


In practice, the MSP will keep running until somewhere in the 1.35 to 1.7 volt section, badly, until the BOR threshold is passed. You can't rely on any data at this point. But if your clock is too high, then the Vcc(MhzMin) is the real threshold.

Then you have to consider the same voltage ranges for the DAC you are using. It will have its own screwy thresholds for proper operation, and for undefined/bad but still operating ranges.