I would likely remain loyal to AA even if MRTC goes away, but from the profitability standpoint there really are pros and cons (it's not a black-and-white decision):
1) It might not help with the retirement of the F100s. If you replace an F100 with an MD80, you already have more seats than the route probably needed.
2) If you get rid of MRTC, you may lose a number of high coach-class fares and have to replace them with really low, bottom of the barrel fares. Even though fares overall are lower right now, I think that some people are still paying premium to fly AA... as evidence, in late April I found that AA's trans-atlantic coach seats were selling at H fares (this is relatively expensive) while UA and others were still at deeper discount fares.
3) On routes where the passengers are overwhelmingly low yield, why not try removing 1st class and replacing it with more MRTC coach, rather than making the coach class LRTC. To me this would be the best of both worlds -- more coach seats to sell, plus keeping MRTC. And on those low yield routes, most likely the 1st class pax are all upgrades that bought low coach fares... not much reason to keep 1st class around in that case.