Is this sentence correct?

1) Would you please help me to find out whether or not this sentence is correct?
>>> But if your boss DOESN’T like it, that COULD be the end of the story.

Shouldn’t it be as below:
>>> But if your boss DID NOT like it, that COULD be the end of the story.
>>> But if your boss DOESN’T like it, that MAY be the end of the story.

2) Instead of ‘could’ as in the original sentence below, what would be the meaning if we used ‘may, might’ or ‘can’?
>>> But if your boss DOESN’T like it, that COULD (may, might, can ?) be the end of the story.

In terms of the meaning of 'possibility,' what is the difference amongst them?

There really is nothing technically wrong with any of the examples you have provided.

You seem to be getting hung up on the contextual meaning of Can/Could and May/Might.

I've answered this a couple of times before, so I'll be brief;

Can/could imply a particular person's ability/desire to do something.

May implies permission needed or granted to do something.

Might implies an ability to do something.