Tom Sullivan wrote a column published in Friday's Denver Post saying his son, Alex, would want him to be there.
Alex Sullivan was among 12 people killed in the July 20 attack in the Denver suburb of Aurora, which also wounded 70 people. James Holmes, suspected in the shooting, faces more than 160 counts including murder and attempted murder.
Holmes has not entered a plea. He is due back in court Monday for a preliminary hearing in which prosecutors will outline their case against him.
Alex Sullivan's widow, Cassandra Sullivan, was among 15 relatives of the victims who said the invitation from theater owner Cinemark to attend a reopening ceremony Jan. 17 was "disgusting" and insensitive.
The families on Wednesday released a letter to Cinemark criticizing the Plano, Texas-based company for not previously offering condolences and refusing to meet with them without lawyers.
"Our family members will never be on this earth with us again and a movie ticket and some token words from people who didn't care enough to reach out to us, nor respond when we reached out to them to talk, is appalling," the letter said.
The 15 signers were related to nine of the victims who were killed.
A spokeswoman for Cinemark had no immediate comment Friday on the letter or on Tom Sullivan's column.
Sullivan's column did not criticize the families who are refusing to attend.
"I will never tell anyone what is the right way or wrong way to grieve the loss of a loved one," he wrote. He offered to support anyone else who does attend.
"The seat next to me will be saved for Alex, but I'll have an extra hand if you need something to hold on to," he wrote.
Sullivan also expressed his gratitude for the outpouring of support his family received from Aurora and elsewhere.
A victim representative for the Sullivan family didn't immediately respond to an email Friday.