A few weeks back due to a very cold spell I moved my two figs (different kinds both unknown) from the garage into the south facing bathroom where both started developing very well. 

Looks like what happened to me when I used MG liquid on my newly rooted trees.  I'll never do it again.  I've talked to several others who had the same experience.  That stuff isn't created for seedlings/new starts, it's like feeding methamphetamine to a baby.

Is the plant doomed? should I "flush" it with some fresh watering?

Mine recovered after 3-4 weeks of regular watering - not overwatering, just regular watering.  I have seen others on here post that you should flush, I erred on the side of caution because I was concerned that overwatering would drown my young tree.  Overwatering has killed far more trees than over-fertilizing (which has claimed zero) for me.  Fertilizer will shock a plant, overwatering will flat out kill it via rot or other means. 

I wish there was a way to get the word out there about liquid fertilizer and young trees, I've tried preaching about it in the past.  I know everyone wants "what's best" for their trees and a lot of folks think, "aw, hell, I want to give my tree the best nutrients possible"... and this happens.  I found that diluting down to 1/4 strength could work when trees hit a certain level of maturity and have a solid root system in place, but I normally don't start dicking around with fertilizers until my trees are filling out root-wise in a 1gal pot.  You're better off just using a slow-release fertilizer mix if you want to go that route - BUT - I wouldn't recommend mixes with slow-release fertilizer until you've at least made it to filling out a nice half-gallon pot (at least)

Looks like too much fertilizer, or too little water, or maybe change in humidity, or too much sun, or ? The bigger question is what is the new growth doing, what is happening at the growing tip. If it continues to put on nice new growth, then it isn't a big deal what these leaves look like. Leaves are a "trailing indicator" - that is they indicate what has happened. The growing point and new growth is a better indication of the course that the plant is on - getting better, or continuing to decline. Even if a plant completely defoliates, as long as it is showing signs of new growth, it is on the right track.