General:
* Outcome
* Result
* Consequence
* Occurrence
* Incident
* Happenstance
* Possibility
* Contingency
* Chance
Formal:
* Denouement
* Issue
* Development
* Circumstance
Informal:
* What happens
* The way things turn out
The best synonym will depend on the specific meaning you want to convey. For example, "outcome" might be a good choice if you are talking about the end result of a situation, while "contingency" might be better if you are talking about a possible event that might happen.