With just 14 minutes left at the Reebok Stadium, the 2011 League Cup winners were staring into the abyss as Bolton led 2-0 thanks to goals from Lee Chung-yong and Lukas Jutkiewicz.
However, Nikola Zigic quickly halved the deficit and with Doncaster on their way to defeat at champions Leicester, the visitors knew just one goal would ensure their survival on goal difference at the expense of Paul Dickov's men.
And Caddis scored in the third of six additional minutes to secure a 2-2 draw and spark wild scenes among the Birmingham support, who Clark dived into to celebrate at the final whistle.
The Blues manager knows he still has a rebuilding job to do in the Midlands with the club reportedly up for sale, at least 10 players out of contract and numerous loanees returning to their parent clubs.
However, the 41-year-old, who conceded he shed tears as safety was confirmed, can at least start that transformation in the Sky Bet Championship, rather than League One.
"I used the word earlier - 'Armageddon', because it's been difficult to attract players to the Championship, so if they went down and there was no fresh investment it would have been tough to attract the players to League One; that was my fear," said Clark.
"I would say it would be a great buy for someone but I don't know what the situation is, I don't know if we're for sale.
"But as manager, for my staff and the players, we need some help, we've got to have experienced players in their prime who've played at this level to contribute and combine with the players that we already have."
Clark typically wears his heart on his sleeve and the emotion of witnessing such a dramatic climax to a difficult year at St Andrew's was still evident in his post-match press conference.
"It's an emotional game, I commit to every job whether I'm a player, a coach or manager," he added.
"I commit to it 100 per cent, I buy into that club and buy into their ethos. I felt for the supporters so much over the last few weeks. It's been really tough for me personally because of that.
"Everything that went through my mind day in, day out, every minute of every day was to do it for the fans."
And Clark conceded that he could not even identify who Birmingham's hero was when Caddis nodded home after Zigic's header had been stopped on the line by Tim Ream.
He joked: "I didn't even know who had scored, I've got to admit. I just saw a yellow jersey going up and it was just mayhem.
"Until I started doing some interviews in the tunnel and they told me it was Paul Caddis...I wondered why the lads were chanting his name in the dressing room!"
Bolton boss Dougie Freedman admitted their late collapse was a microcosm of their entire season as they finished 14th in the table despite only missing out on the play-offs on goal difference last term.
"We felt we didn't perform anywhere near where we have been in the first half, I didn't think the energy wasn't there," said the ex-Crystal Palace boss.
"In the second half we got off and running, went a couple of goals up and we didn't kill the game off. When you don't kill the game off in this division you give the opposition confidence.
"Because of the occasion it feels like Birmingham have won the league. But we've dropped points in too many games at home this season."