To clarify: This reads like you're back at work after vacation or something. In that case, why do you need people to tell you? Unless you have a secretary, it's your responsibility to check what's going on at your work.

You have been gone where? Fired?

Did you leave the job for good, or have you been on vacation? Also, if it was mandatory, why weren't you told? Also also, what kind of job do you have where the staff get together for dinner? I've only ever had dinner with one colleague, but that's because she's also my roommate.

Was it mandatory? If not then who gives a fuck if you were at the dinner or not.

Even if on vacation it is still your responsibility to check especially if you were at home and could've gone. Employers are not going to personally tell every employee. You are supposed to call in check or stop to see if anything was posted.