"For us as parents, it's the middle-of-the-night call we all dread," his mother, Sherry Cassedy said of the predawn phone call that notified them of the accident, involving a backward fall off a skateboard while Sullivan was returning from a party.
Sullivan, a sophomore at the University of California, Santa Cruz, and a 2008 graduate of Gunn High School, remained on life support at Valley Medical Center in San Jose until Wednesday night, when doctors removed his healthy organs for waiting recipients.
"He's a young, vibrant healthy body from the neck down and, hopefully, his healthy body will allow others to sustain their lives and he will live on in those people," Cassedy said Monday.
Cassedy and Sullivan's father, Matt Sullivan, spoke in an interview in the back yard of their Maureen Avenue home, where Tim grew up and attended Fairmeadow Elementary, Jordan Middle and Gunn High schools.
Sullivan was taking upper-level math and German courses at Santa Cruz and had just learned he had been accepted to study at the Free University of Berlin next fall, his mother said.
"He was so excited about it. He was trying to get his German to the level where he could study and take classes in German in Berlin."
Sullivan was an athlete, having played soccer and baseball at Gunn.
He loved skateboarding, Hacky Sack, surfing and "just playing, just being out in the world," his mother said. "He was just a very fun-loving, open-hearted person."
Cassedy and Sullivan had visited with Tim, the youngest of their three children, Saturday evening at his home in Santa Cruz.
"We spend some time in Santa Cruz since he's been there, and we stopped by their little house to say hi and chatted for a few minutes," Cassedy said.
"We went off to the movies, and they went off to a party later on.
"I think we've really instilled the message that you don't drink and drive, so if you're going to a party you don't drive," she said.
Sullivan's roommate was on a bicycle and Sullivan on his skateboard, without a helmet, when the accident occurred around 3 a.m. Sunday, she said.
"He had just come down a hill in Capitola and was moving pretty fast when the board came out from under him. He fell backwards and hit hard on the back of his head," Cassedy said.
He was airlifted to Valley Medical Center. His roommate called Cassedy and Sullivan, who drove to the medical center, arriving at about the same time as their son.
"From the first consultation we had with the emergency doctor, the trauma doctor, he was not optimistic about Timmy's survival at all," Cassedy said.
Sullivan never regained consciousness, his mother said.
"You dodge so many bullets during your parenting years where they survive a near miss," said Cassedy, a longtime family lawyer and mediator in Palo Alto.
"I think we just feel really blessed to have had 20 years with him, and that's what we want to really hold onto and focus on.
"Sometimes you can sit and talk about it rationally, and then that all goes out the window and you're hanging on by your fingernails and it shifts again.
"We're just putting one foot in front of another until we can move into a future that until now seemed unimaginable."
Cassedy and Sullivan said they hope to meet the recipients of their son's organs. The donation process is anonymous unless both recipients and donor families choose to meet.
The family plans a memorial mass today, Friday, at 7 p.m. at Our Lady of the Rosary Church, 3233 Cowper St.
A celebration of life will be held Saturday at the amphitheater at Gunn High School, 780 Arastradero Road. Family and friends are invited to gather at 2:30 p.m., with eulogies beginning about 3:30 p.m. and ending by 6 p.m.
In addition to his parents, Sullivan is survived by his brother, Tyler, of Santa Cruz; his sister, Cassedy, of Portland; his grandmothers, Alma Sullivan of Woodside and Paddy Cassedy of San Jose; and many aunts, uncles and cousins.
Rather than flowers, the Sullivan family asks that memorial contributions be made to the Timothy Sullivan Legacy Fund of the Silicon Valley Community Foundation, 2440 West El Camino Real, Suite 300, Mountain View, CA 94040.