There are two recalls on the mustang,
1.) Dec 2014 - 14B09
2.) May 2015 - 15S21
The 14B09 part is an interim part that Ford released to replace the inflator. Then they recalled that with the 15S21, which at present has no time to delivery.
I also have a Honda Fit which is also has the same takata airbag recall. In this case, Honda is taking it a bit more seriously and has offered/ issued loaner/rentals (through Enterprise on 30 day consecutive contracts) to some of it's 6 million customers affected. At present I have one of the rentals courtesy of Honda.
To my knowledge, and my local dealerships knowledge, Ford has not offered this, and the service manager I spoke to was shocked Honda was offering long term rentals.
If your mustang, like mine, is purely a garage queen and not a daily driver, risk is somewhat mitigated... If it's your DD, risk inherently increases, especially in regions affected by heat & humidity (as was found to be the RCA). I would take it fairly seriously. The stories of the victims who survived are devastating.
There has been lots of talk on Mustang / Honda forums about depreciated values of cars.
Dealerships and used car dealers have been instructed NOT to sell vehicles under this recall. Honda has even offered a trade-in depreciation incentive for those that want to trade their vehicles for new Honda's.
If you were looking to sell or trade your Mustang, now would be a bad time. After the parts are replaced I don't see the recall as a depreciation factor if proof is provided that it's been remediated.