B717 - unknown; indicated they intend to fly 30-45 out of the 91 through 2022. They are leased aircraft and facing a airworthiness directive to replace the seats by the end of 2022. No confirmation they intend to fly these beyond 2022 at this point. Rumors of trying to get Boeing to take them back for a down the road MAX order but nothing but rumor months ago.
B73G - announced today retiring the small subfleet of 10 aircraft by the end of 2020; the aircraft are in the 10-12 year range and likely facing near-term expensive heavy maintenance checks, otherwise they'd probably stay. Likely to be able to sell and generate some cash at some point
B738 - staying; some frames may stay in storage for awhile until demand recovers and/or if facing heavy maintenance checks
B739 - new staying; these will all return to service sooner rather than later, a few of the earliest deliveries may be approaching their first heavy maintenance cycle
A319 - staying; some frames may stay in storage for awhile until demand recovers and/or if facing heavy maintenance checks; these aircraft are 17-21 years old and still have life in them
A320 - a portion of the fleet to be retired in 2020, they are essentially retirement pull-aheads. Some combination of age and any facing near-term heavy maintenance. Others will continue to fly
A321 - new and staying; these will all return to service sooner rather than later
A220 - new, they are the future of the small narrowbody fleet
B757 - some rationalization of the fleet likely to occur, nothing announced yet but some of the older subfleets particularly non-ETOPS may face earlier retirement.
B753 - these will stay for the near term, most just went through a heavy maintenance cycle in the last 1-2 years, needed for hub-to-hub capacity
B763ER - a portion of the fleet to be retired in 2020, they are essentially retirement pull-aheads. Some combination of age and any facing near-term heavy maintenance. Others will continue to fly
B764 - nothing announced yet, but potential for the unmodded frames to face early retirement; this fleet is mostly in storage currently
B77E/L - all to be retired by end of 2020
A332 - could potentially be a candidate for retirement, but not yet announced anything, small subfleet but commonality with A333 and A339
A333 - staying; some frames may stay in storage for awhile until demand recovers and/or if facing heavy maintenance checks
A339 - new, they are the future of the widebody fleet
A359 - new, they are the future of the large widebody fleet
MD88 / MD90 - already retired and removed from service