User error.
You should always turn the battery device off or go into "standby mode" when you put it in a purse or pocket or bag. (Usually 5 clicks on the fire button) If left on, the fire button can be inadvertantly pressed by objects in the bag. This may over-discharge the battery, causing it to overheat and go into failure
Regulated mods generally have a safety feature to prevent this, a self auto timer that makes the mod stop firing after 10 - 15 seconds. But that means it can be pressed again and start the process over again, eventually overdischarging the battery. I am probably biased, but I've seen a lot of issues of this type over the years with SMOK products.
I personally would retire that mod. Hard to tell what wire circuitry or board has been ruined. Expensive lesson learned here.
The tank may be salvagable. You would need to replace the old coil. You may also need to clean and soak the entire tank in isopropal alcohol, rinse well in water, and allow to air dry. Make sure to prime the new coil well with e-liquid prior to putting it in the tank.