Vince McMahon was said to be "adamant" that Ric Flair not violate his 2008 retirement storyline, but WWE did let Flair get physical in the ring during his RAW appearance after undergoing medical tests and an EKG earlier in the day.
WWE isn't all that concerned with the TNA lawsuit and don't view it as any sort of significant threat. They haven't heard anything from TNA on the lawsuit front in months, which led to WWE making the call to bring Flair in. The issue is - they're not signing former TNA talents to actual contracts until the lawsuit is settled. That's the reason Flair is not currently under contract with the company.
Also, we posted the following on December 20, 2012:
WWE did not promote Ric Flair's return on Monday, likely due to the ongoing WWE vs. TNA Lawsuit. This is also likely the reason that Flair has not signed a contract with WWE. While Flair was on RAW Monday night, RAW viewership rose from around 4.1 million viewers to 4.7 million viewers, with big spikes in the key male demographics.
The return was planned for several weeks, with several angles for him being pitched, including one where he would introduce his daughter, Ashley, who is currently training at NXT as Charlotte.
Flair initially was not going to be doing anything physical, but those plans quickly changed. When Flair arrived in Philadelphia, he was ordered to undergo an EKG to make sure his heart was healthy enough for him to get physical on RAW with Punk, Heyman and The Shield. The return was kept a secret from the crew, and while there was buzz internally that he could appear, he was kept in a trailer away from everybody else.