It really depends on the job, the context and innumerable other factors.
So no, it's not a given that you would be sacked.
There are employment policies and procedures and also nuance.
Blackmail is a criminal offence but not always one that is easy to report.
I was sexually assaulted by someone that in my line of work, I should not have put myself in the position to be assaulted by.
But I fucked up, and i did and they threatened me and controlled and further assaulted me for months because they knew that I wouldn't report them because it was my fuck up in the beginning that allowed it to happen.
And even though they knew the law and my employer would be on my side, they also knew I felt so ashamed that I wouldn't want to ever report it and go through the humiliation of having to tell people what they did to me and how it was all my fault that I put myself in that position.
What ended up happening was my employer heard a rumour but not a complaint, which I was questioned about and it was investigated and I was seen as a victim and was encouraged to report it to the Police. Which I didn't because of the shame, trauma and humiliation.
But it did stop him being able to further abuse me.
Lots of things happen that aren't as clear cut as we would like them to be.