I have an idea for an epic maneuver that a wizard could perform as a last resort in certain emergency situations. A severely wounded wizard could, if there is something of much greater utility then his own life on the line, transfigure himself into a healthy version of himself in order to continue the fight. This would be a death sentence, but still worth it if the stakes were high enough.

Then again Harry can already sustain a small transfigured object even in his sleep. Perhaps the most powerful of wizards could sustain a transfiguration on their own body indefinitely. Or... Professor McGonagall said that it would be possible for a child to transfigure themselves into an adult bodily form. Perhaps if the wizard could not sustain an object the size of their own body indefinitely after the emergency situation has passed they could again transfigure themselves into a adolescent, child, or midget form in order to achieve a body with a volume that they could sustain. Unless doing another transfiguration would cause the consequences of the previous transfiguration to be imposed on the new form. Though I don't see why that would necessarily be the case.

This would be a very fragile sort of existence. They would be much weaker due to the constant drain on their magic and incapacitation or anything that dispels the transfiguration would result in death.