If the same accident is repeated, it is no coincidence.
If the same accident is repeated, it is fate.
These are both fine. It might be slightly more natural to say: "If an accident happens twice/more than once, it is fate/no coincidence."
If A coincidence keeps repeating, it is fate.
If A coincidence WAS repeated, it WAS inevitable. (This is better in the past tense I think.)
And perhaps: If teachers fall every time they enter classroom 102, they are meant to fall when they enter the room.
If someone else contradicts me, they are probably right because I am in a rush to get to work. Sorry! I hope it helps though!