Is there any canon or EU explanation on what happened to Sabé after the events of Episode 1? I would assume that she most likely went on to pursue further undercover missions as a decoy.
Main (Disney) Canon
We learn in the (canon) novel Star Wars: Queen's Shadow that after Padmé became a senator, Sabé continued to work for her, mainly liaising with the Naboo intelligence service (to help root out any plots against the Senator) but also as a pilot.
“I have been working as part of the senator’s security detail on Coruscant,” Sabé informed the queen. “Along with Captain Tonra, I have been undercover in one of the capital’s seedier neighborhoods, gathering intelligence on the public opinion of Senator Amidala.”
The last canon mention of Sabé is that after the death of her friend (and former employer) Padmé Amidala, Sabé was planning to travel to Coruscant under her previous cover in order to find out the truth behind her untimely demise. Before she could leave she was contacted by Bail Organa.
“I’m going to find out what happened to my friend,” Sabé said. She got up and began to pace the small room. She couldn’t sit still anymore. She couldn’t stay on this paradise of a world while there were dreadful secrets for her to uncover. Cordé was dead. Versé was dead. Obi-Wan was dead. Master Billaba was dead. Anakin Skywalker was dead.
Padmé Amidala Naberrie was dead, her dreams with her.
“I’ll go back to Coruscant,” she said. “I’ll be Tsabin a little bit longer. One or two of our old contacts might still be there. They might know something, and that would be a place to start.”
Sabé held the device in her palm and activated it, calling up a familiar figure. When she spoke, it was in Amidala’s voice. She had no intention of giving anything away.
“Senator Organa, now is not a good time,” she said. “What do you want?”
The clear implication is that she would go on to become one of the early members of the Alliance to Restore the Republic.
According to the Star Wars: Force Unleashed Campaign Guide, Sabé continued to serve the Naboo state as an intermediary with the Galactic Senate and later, as a covert operative of the Campaign to Restore the Republic, ultimately (and highly coincidentally) serving as a teacher to Leia Organa and her sister Winter.
The former handmaiden and bodyguard for Padme Amidala pursues a similar career after the Clone Wars, working as a diplomatic agent for Naboo's rulers and a clandestine operative for the resistance movement among various Imperial Senators and insurgent groups. After the Clone Wars. Sabé continues her service to the Naboo govern¬ment as an aid to its representative to the Imperial Senate. Angered by what little she knew of her friend Padmé Amidala's death, Sabé identifies and cultivates contacts in the Senate and on sympathetic worlds who secretly opposed Palpatine's tyrannical rule and the Empire's oppressive policies. While walking the corridors of the bureaucracy she quietly aids the resistance, relaying messages between agents, gathering, analyzing, and disseminating intelligence, guarding against Imperial treachery, and counseling those who are seeking to channel aid to freedom fighters around the galaxy.
As a diplomatic emissary, Sabé has official access to transportation, not only between Naboo and Coruscant but to any worlds that have business, negotiations, or ties with her homeworld. This mobility enables her to expand her secret resistance activities beyond the Senate chamber; she smuggles equipment to nascent insurgent cells, conveys intelligence about Imperial operations, and trains freedom fighters in combat and espionage.
During this time, she befriends Senator Bail Organa and becomes one of his principal agents carrying out operations behind the scenes. She makes many trips to Alderaan to check in on Amidala's daughter, now Organa's adopted daughter, Leia. Organa encourages Sabé to tutor Leia and her close companion Winter in a variety of subjects, from etiquette and bureaucracy to the more esoteric arts. Though Leia learns much from Sabé, Winter spends more time with her, improving skills that later serve her well as Leia's double and bodyguard.