Flipping the keyboard is unlikely to be advantageous to someone forced to use their left hand.
It's your brain that locates the keys to be pressed and coordinates your hand and finger into position. This has nothing to do with whether you are left or right handed or are forced, in some other way, to use your less dominant hand.
If you pass your phone to your less dominant hand and attempt to type a 'Q' you will still automatically reach for the top left area of the keyboard because that is where you have learned to find the 'Q'.
The only effect that flipping a keyboard will have is that you will have to re-learn the locations of the keys and practice for a long time in order to be able to type at normal speed.
If you want to experience the amount of disorientation changing the keyboard layout gives, try switching to a 'Dvorak' layout and see how long it takes you to get up to normal speed.