Only one I can think of off the top of my head is Omaha. I know both Philly and Brookfield had plans, but neither plan really got anywhere.
Brookfield was actually planning to renovate their elephant habitat years before they went out of the species (Strahl described the plans as "seven years away" in 2006) and was intended to follow Great Bear Wilderness and a "new children's zoo" ; a few years after that the facility was running out of money and being threatened with multiple tax hikes, which probably contributed to elephants leaving the zoo, as well as the losses of hippopotamus, congo buffalo and warthog around the same timeframe. The new children's zoo was considerably drawn back into Wild Encounters, which was the last project under Strahl. I'm not sure the current administration position yet so it could very well be off the table now, but Brookfield spent over a decade essentially limping through projects already scheduled to come before the elephant renovation, which I think is part of why they maintained their intent to bring them back for so long.
Four zoos that come to mind that phased out elephants then brought them back a few years later are Omaha's Henry Doorly Zoo (no elephants from 2011-2016), Birmingham Zoo (2007-2011), Tampa's Lowry Park Zoo (1993-2003), and Lincoln Park Zoo (2000-2003). Lincoln Park however, has since gotten rid of elephants once again.
Longleat Safari Park moved their herd of african elephants to France in 2003, then rescued Anne the UK’s last circus elephant in 2011.
The panelists at Brookfield's master plan symposium said that while they couldn't make any guarantees elephantwise, they do have an idea as to how to bring them back in a dynamic way - having visited National Zoo and being thoroughly impressed with Elephant Trails. @pachyderm pro can give a more definitive answer than I can. Oklahoma City Zoo sent their elephants to Tulsa temporarily when they were building their new elephant habitat, so there was a period of time when there were no elephants at OKC. San Antonio has been adamant that elephants will return after they complete their gorilla project in 2025. Reid Park had a very brief period where they swapped Connie and Shaba for some of San Diego Zoo Safari Park's elephants when that matriline naturally split up. Nashville has shown intent for bringing elephants back, the main issue being the availability of elephants.
You summed it up nicely. The panelists suggested that the zoo does in fact have a concept in mind for a future elephant complex that will be shown when the master plan is released, although do keep in mind this was last Summer and things could've changed since then. Barring any further delays, we'll finally have a definitive answer on this age old question within the next two months.
Cleveland Zoo sent their elephants to the Columbus Zoo while they built a new elephant area, so that doesn't really count as "going out of elephants" because it was a temporary move with a known return date.
