Luke (Mark Hamill) might not have physically left Ahch-To to fight against his lost estranged nephew, Kylo Ren (Adam Driver) on the mineral planet of Crait in Star Wars: The Last Jedi , but the Jedi Master did actually think of leaving the planet to rejoin the Resistance with Rey (Daisy Ridley).
According to the novelization of Lucasfilm's latest sequel trilogy installment (via Screen Rant), Luke actually wanted to join Rey to help the Resistance. The book reveals an additional scene in the film where Luke reawakens the Force inside him while Rey goes on to explore the Dark Side cave on Ahch-To. After closing himself off from the Force so long Luke ends up realizing how important it is for him to return to Leia and the Resistance and join Rey.
Walking back to the village, Luke calls out for Rey, saying "I'm coming with you."
However, Luke finds Rey in the middle of a "Force" bond between Kylo Ren and Rey, and after fighting over the possibility of Ben returning to the light, Luke ended up changing his mind. While the Jakku orphan strongly believes that Ben can still turn back to the light and become a valuable ally to the resistance, Luke believed that his nephew was totally lost to the Dark Side.
The only question left now is whether Luke was really right, or whether Kylo Ren will still be redeemed in Episode IX. Let's wait and see.
Star Wars: Episode IX premieres December 20, 2019. Star Wars: The Last Jedi is getting its Digital HD release on March 13 and its Blu-Ray and DVD release on March 27.