Over a 15 year period, I have done Shackled City, Age of Worms, and Savage Tides. I'm on chapter 11 of Savage Tides and already thinking about what to do next, since my players find D and D the most fun part of the pandemic. Is there something like them, but for Fifth edition?
Alternatively, with their epic level characters, they might get into high level campaigns against Hades or canonical gods. Is there a prewritten campaign where PCs fight Greek gods, or on what Graz'zt was goind with Lolth?
Chapter 11...impressive, how often do you and your players meet? Once a week?
Grazzt and Lolth and the events going on there roughly around the same timeframe as Savage Tide is in the 3.5 adventure Expedition to the Demonweb Pits.
WotC has been putting together their 5E big adventure books that are comparable to APs if not quite as large a range in levels.
And I have heard of Odyssey of the Dragonlords, from Modiphius, as a pseudo-Greek campaign AP that extends into epic. Mixed reviews about that one.