Nikki's husband Craig Sadler posted a heartfelt letter on Facebook in Nikki's memory on Saturday, revealing his wife had "suffered an aneurysm" several days earlier on October 28 but remained on life support so her organs could be donated.
"Many of you already know something is wrong. The love of my life Nikki Sadler suffered an aneurysm on Wednesday. She would already be gone, but she's an organ donor and has been kept on life support to make that possible," Craig wrote alongside a beautiful black-and-white photo of the singer sitting in front of a drum set.
"That shouldn't be a surprise to us. Even at the end she is still giving. She was so loved that I know thousands of you will be grieving with us. There are only a few hours left for me to hold her hand and kiss her forehead."
Due to the ongoing coronavirus pandemic, Craig apparently wasn't able to make typical funeral plans.
"The current Covid situation won't allow the huge service that she deserves, but I would like to offer you the opportunity to honor her. She will be taken to the OR at 3:00 am Central time to give her final gift that will save the lives of strangers," Craig continued in his post.
"You probably know she practically worshiped Stevie Nicks. Before they begin, they will play 'Landslide' for her one last time. If you are able, you can pause at 3:00 wherever you are and listen to it with her. She will know that you're sharing her farewell. She loved so many of you and I know you loved her too."
Justin wrote a touching tribute to Nikki on Instagram one day after learning the sad news.
"[Nikki] was a fiery, funny lady who could sing the Hell out of a rock song with the same kind of ease and command she lovingly used to cut you with her twangy Southern wit. Even in our 20's when we were on American Idol together I could tell that she'd had a challenging life, and that not that many people had been kind to her along the way," Justin wrote.
"But I'll never forget the day that her idol, Stevie Nicks, sent her flowers with a card that said 'You are the Gypsy that I was...'. Nikki was on cloud nine and the joy and excitement that radiated from her was infectious."
"After the kind of emotional beating she took at the hands of the masses, she deserved to feel good about herself, even for a little while," Justin added.
Nikki previously said she had received backlash for outlasting Tamyra Grey in the American Idol competition. Some Idol fans allegedly told Nikki to kill herself and called her "a fraud," and her short-lived job as a stripper made headlines after the show, according to People.
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"Rest well, 'Gypsy'...and thank you for the laughter, merciless teasing, strength, vulnerability, love and friendship you showed me during our time together in the spotlight. #rip #americanidol," Justin concluded.
American Idol also commented on Nikki's unexpected death Sunday on Twitter.
"Nikki McKibbin was an incredible talent and we are deeply saddened by the news of her passing. She was part of our American Idol family and will be truly missed. Our hearts and prayers go out to her family and friends during this difficult time," the show tweeted.
After her appearance on American Idol, Nikki battled her demons -- some of which she struggled with prior to becoming famoust -- on Season 2 of VH1's Celebrity Rehab with Dr. Drew in 2008 as well as the show's spinoff Sober House.
"I came out of Idol with a lack of self-confidence," Nikkis told Us at the time, adding, "I had never been told I wasn't good enough."
However, that changed when Nikki competed on Idol and was exposed to Simon's arguably harsh criticism on a weekly basis.
"Having to hear it for so many weeks from Simon Cowell killed me inside. I couldn't get the sh-t he had said to me out of my head," Nikki had recalled.
"It drove me deeper into my depression. I wouldn't say that this was Simon's fault. It just added to the addict that I already was."
According to Nikki, who had also revealed she was abused as a child, her troubles began when she followed in her mother's addiction footsteps and became an alcoholic at age 16.
"I don't remember a time when I didn't drink after that -- except when I was expecting [my son] Tristen [when I was 19]. In didn't even smoke when I was pregnant! By the time I was 21, I started stripping. It was fun for a while... [but] if I was working I was drinking," she explained.
From there, Nikki said she also became addicted to Ecstasy.
"Back in high school, I had tried pot and acid, but soon I tried Ecstasy and quickly became addicted [and] was stripping to support my habit," Nikki told Us at the time.
"Between myself and two others, we were spending almost a thousand dollars a day."
Nikki's Ecstasy addiction ended after a cousin intervened, however her alcohol addiction continued. Nikki apparently managed to keep her alcoholism a secret from Idol producers while on the show.
But after American Idol's inaugural season came to a close and her deals with 19 Management and RCA Records didn't work out -- they allegedly wanted to make her a country singer while she wanted to remain a rocker -- things got even worse for Nikki.
"I was buying pot for somebody, and the dealer gave me a bag of cocaine. I wanted to try a little, so I went to my mom. She's my best friend... [and] always said 'If you want to try it, try it with me, just don't make it a habit,'" Nikki shared.
"It went out of control from there... in less than a year and a half, I went through $250,000 -- my residuals from Idol and the tour and my settlement with RCA."
Nikki said she hit rock bottom in February 2008, when she ended up in a psychiatric ward after she drank "half a gallon of vodka" and swallowed 18 painkiller pills in an incident she has denied was a suicide attempt.
"I broke my foot [and] I was home alone and I kept taking painkillers," Nikki had told Us. "At the time I didn't realize I was allergic to the medication."
Nikki later told People she got addicted to painkillers as a result of having multiple back surgeries for herniated discs.
"It's still a struggle every day. For a long time, I wasn't taking care of myself," Nikki explained to People last year.
"I wasn't being the person I should be. I'm in a better place now... But now people always assume that I'm on something even when I'm not. I get it, though. I lied so much and was in such denial that how can you possibly believe me? I get it."
Nikki called her husband Craig "an amazing man" in her interview and gushed about Tristen, who appeared on American Idol in 2014 but was eliminated after the auditions round. About The Author:Elizabeth Kwiatkowski
Elizabeth Kwiatkowski is Associate Editor of Reality TV World and has been covering the reality TV genre for more than a decade.