A worker gets an email that he won a million dollars but his boss wants to steal it from him so they agree to battle each other in a nerf gun war.

This may be a scene but not a whole plot.

As a short it lacks plausibility most people now days would not believe from a mere email that they have actually won a million dollars and if they do they loose any credibility in the audiences mind.

Secondly as stated above if the MC gets undeniable confirmation that he has won then why not quit his job and tell the boss to stick it then keep his money.

Hope this helps.

Sure, how wan they "agree" on this? this must be clarified in the logline.

Most people would go to the cops, not agree to give it up to someone wanting to play a game. Why does he agree to this?