So this is from oneworld:
https://www.oneworld.com/news/2019-0...ement-on-LATAM
oneworld statement on LATAM
26 SEPTEMBER 2019
LATAM advised
oneworld earlier today of their decision to partner with an airline outside of the
oneworld alliance. LATAM further advised
oneworld that they intend to leave the alliance in due course and in accordance with formal contractual requirements. We are disappointed, but we respect their decision. They have been a valued long-term member of the alliance, and we wish them well.
Our priority at this time is to our customers and while LATAM remains a member of
oneworld, the full customer benefits will continue to be delivered. As the transition continues, we will work to ensure a seamless experience for our customers.
oneworld remains a strong coalition of high-quality airlines. There has been significant progress in member airlines deepening their bilateral relationships, as evidenced by the recent regulatory approval of the American Airlines and Qantas joint business.
Someone on the AA forum stated it's a 12 month lead time to leave OW (Aer Lingus announced May 30 2006 and left May 31 2007). I assume DL/LATAM will forge an earlier bilateral FF agreement so that there are some benefits ASAP and then they'll solidify when they formally join ST.