I am not familiar with that part of the game (I think I took the other route ;) but usually in battles where you are outmatched, you can just run away. Once you are far enough away, you should "disengage" and be able to fast travel to safety. Running into a camp or town also usually helps. If you have party members still alive you should command them to disengage so they run with you and don't kite the enemy to you (using voice commands on xbox I just shout "everybody disengage", helps with a dragon or two I wasn't ready for yet).
I haven't encountered many battles where I was locked into an area and couldn't run away, although it often feels like that is the case based on the urgency of the plot that is happening around you. Although I haven't tried running away from every battle so maybe there are some. If you are truly locked in an area, then you have 2 options remaining.
First, I would look back at your saves. Sometimes (often) there is an autosave not long before you got into trouble. Use that, then fast travel to a more level-appropriate area.
The last suggestion I would have if all else fails, is to change the difficulty to easiest (you can change this setting mid game any time and change it back later), grind through the part, then get out of there.
Once safe you should probably go somewhere else and level up a bit more. I have found this game to have a lot of guesswork in terms of what level you should be at for an area, but it hasn't bothered me too much so far. As long as I can come back to it later; plus usually when that happens it means you're skipping a more fun new area that is level appropriate, so I go back and look for that.