[HTC EVO 3D] Sad Panda:
Hi there, happy to attempt to answer your question. First, some background. Water will damage electronics in two ways. The first is the scenario I described before, the device still has enough liquid to carry charge when electricity is applied, and two points of contact short in a place that the electrical engineers that designed the circuit had intended. It may or may not be a short that is in a place, or Carries a powerful enough charge to physically damage the device. However this is why it is so important to remove power as quick as possible.

The second way is if the water, and oxygen in the device are capable of eroding the material the water and oxygen comes in contact with. Erosion is a slower process than the other damage, but still there are variables we can't account for. It would be dependent on how much water and oxygen make contact, ambient temperature, and the chemical makeup of whatever material we are talking about. Erosion happens from water, and oxygen, oxidizing the material. In other words chemically changing the constituent atoms of the material into a different compound. Rust of iron is an example of the erosion I am explaining.

And now for the substance of the post. Because of the micro architecture of these devices we don't have much original material to work with. If the erosion only takes away the top layer of a material then you will be fine once you stop the erosion process. If the material that was eroding has completely degenerated you may not be able to save the device without replacing something.

A mild solvent can be used to remove what has already been eroded, and if the solvent has high affinity for water we can stop any future erosion. Yes, the solvent itself can erode material, but if we find a solvent that does the forementioned and is volatile in air, the solvent will evaporate very quickly, much quicker than water ever would. Isopropyl alcohol (remember find the highest concentration of alcohol to water you can find) just happens to have all the desired properties we want, and is mild enough to prevent further harm.

So my long winded answer in conclusion is, maybe. If power was cut before a devastating short, the water that hasn't already evaporated hasn't eroded something beyond disintegration of enough material to cease to function, and we can use the alcohol to dissolve enough debris to avoid an electrical short in the future, then yes you will bring your device back to life.

I think you might be ok if it has been a week or so. If the device just won't power on you have nothing at all to lose in trying. I had a device like you mentioned (the my touch 4g) that my cat knocked a full glass of water onto, stayed powered on until I woke up to find it in the morning, sat for two months. I dismantled it and submerged all the parts into alcohol for twenty minutes, swirling vigorously. At the end you could see dust, and oxidized material dissolved in the alcohol that had been in the device. After 24 hours of the alcohol drying it powered on, the only thing that didn't function was the SD port.

So yes I really do believe you may have a good chance of resuscitating your device, even after the time past.