Professor Oak will be encountered later in the series. He will live in pallet town, although he will be named many times throughout the story before. When he will be encountered with, it will be revealed that people refer to Gary now when they talk about professor Oak, since he has taken up the title as well as his grandfather's laboratory.
Gary was married to Melissa, the trainer who defeated him in the Indigo League, but after his family disappeared, he left to go search for them. Although she protested and wanted to go with him, he wouldn't put her in danger so he sneaked off at night.
When Articuno succumbed to the curse, it went on a rampage and destroyed Cinnabar and the Seafoam Islands. Without an end to its rage, it headed towards Pallet, where numerous buildings were also destroyed and people killed. Had it not have been for the combined efforts of Ash and Gary, the destruction would have been worse. Articuno retreated to its lair back in the whirl islands, and everyone feared for its return. During this battle, Ash's house got destroyed and his mother was hurt when a wooden plank fell on her back. Although she survived, she would never walk as well as she once would.
The other residents of Pallet slowly abandoned the city as time passed, fearing for a second attach.
Gary, on the other hand, and his wife, Melissa, decided that they would stay and protect their hometown. Delia and Sam decided to stay too. They figured it would be best as they could fight Articuno if it showed up again, and stop it before reaching other more populated towns.
Years later, Articuno exited its lair again. Gary and Melissa decided to go face it south, before it reached the city, both to protect the city itself, and to minimize the damage to the areas below. Articuno was once more pushed back, but when they returned, their family was gone.
Shortly after, Gary decided to go off alone looking for his family, who were captured by Team Cipher and forced Sam Oak to work in one of their labs, threatening to kill Delia and his granddaughter if he refuses.
Gary figures out his family has been kidnapped but doesn't know by who, so he spent almost a year looking for them.
At some point, Vergil comes across Gary, and he, Cole and Gary bond and travel together for a while.
Gary takes part in the battle for Saffron. He is betrayed as is everyone, and stands his ground until the end. He loses one or two pokemon during the battle, and gets wounded while escaping. He also helps some trainers escape too. It is from one of these trainers that Vergil learns Gary is alive.
At some point, Team Cipher will start expanding and hire muscle. Both Vergil and Gary will pick up on this trail and look into this, believing that Sam Oak can possibly be behind this "game changing technology" that the goons were hired at.
When they get close, Cipher will ask Oak for something that will give them advantage over Gary, threatening to throw his sister down a balcony. However, Gary's sister prefers to die than pput her brother in immediate danger, so she breaks free and falls to her death. Her final words are "Dont tell them anything" to her grandfather. Sam is devastated by this, but soon he is freed by his grandson.