Warning: SPOILERS for The Walking Dead season 10, episode 13.
New details about what happened to Rick Grimes after Andrew Lincoln exited the series have been revealed in The Walking Dead season 10, episode 13, "What We Become". Lincoln was quite literally the face of the Walking Dead franchise, having been the main star since it premiered way back in October 2010. However, after spending years filming throughout the summer months in Georgia, Lincoln wanted to spend more time with his family in England. So he left the show but planned to return in three Walking Dead movies.
It's unclear what AMC and Universal are doing with those movies at this time, but to catapult the story forward, Rick disappeared in The Walking Dead season 9, episode 5, being taken in a helicopter by the CRM group, heading to an unknown fate. Since then, The Walking Dead has time jumped over six years forward. What Rick has been doing in that time has been a mystery, but thanks to Danai Gurira's final episode as Michonne, Walking Dead fans now know a little bit about what actually happened in those years.
In The Walking Dead season 10, episode 13, "What We Become", Michonne discovered Rick's old boots - the ones he's worn throughout the entire series - among Virgil's things. That's when she forced him to take her to where he found the boots, which is how they ended up on a deserted ship. It's there that Michonne discovers Rick survived the explosion on the bridge. Among the various items, there was an iPhone that had a drawing of Michonne and Judith on it, with Rick's name etched at the top.
It makes sense that the producers would have Rick's name written at the top of the phone, just so that there wouldn't be any confusion regarding who the device belonged to. What's interesting is that RJ wasn't drawn on the phone next to Michonne and Judith; the reason for that is because Rick never met RJ. Michonne was pregnant when he disappeared, so he never knew his son - or the fact that he had a son and not a daughter.
While specific details weren't shared regarding Rick Grimes' current whereabouts, what was revealed was enough to confirm that Rick was either working alongside the CRM group or escaped to go back home, to his family that he certainly didn't forget about. Furthermore, it confirms that he was still in the general vicinity, though he perhaps didn't know exactly where he was. In the end, these teases are meant to setup the Walking Dead movies and act as a springboard for Michonne's next story arc - one that takes her away from the mainline show.