They'll have a real hard time proving likelyhood of confusion when Independence Air no longer exists. The public's understanding is that it went bankrupt and is defunct. The public hasn't seen that mark for like 3 years, they're not going to be confused because there's nothing to be confused
with. How do you confuse A, an airline that used to exist, and B, a fake airline in an online game, when A's marks, logos and whatever else is no longer around?
Frankly the people who are more at risk are the people using names of airlines that are still in existence. Moreover the Independence Air trademark was ABANDONED.
"A trademark is abandoned when its use is discontinued with an intent not to resume its use. Such intent can be inferred from the circumstances. Moreover, non-use for three consecutive years is prima facie evidence of abandonment. The basic idea is that trademark law only protects marks that are being used, and parties are not entitled to warehouse potentially useful marks."
Source: Harvard Law School http://cyber.law.harvard.edu/metaschool/fisher/domain/tm.htm#6
The airline went bankrupt in 2005, and since NWA hasn't used the trademark for the past 3 years, that's sufficient evidence that it's been abandoned under US Trademark law.
And these are airlines, not the RIAA. They don't sue dead women or 13 year old girls.