From the very start only Carol and Daryl. then other long living characters are- Rosita, Eugene, Judith, Micchone and Gabriel. Other than that not a lot. Maggie left the show open ended and is in negotiations to come back.
The Negan / Saviours, which coincided with Scott M Gimple being the showrunner really did knock TWD for a while. Now there's a show runner in place who has taken it back to nearly matching it's best. It's interesting, as FTWD has also seen a sharp decline in quality over the last season. There's also another spun off due in 2020, plus the Rick Grimes "Movies" I just hope they compliment the main TV programme, as currently it seems to be somewhat diluted.