Well, at the end of the day, one of the advantages of using events is the asynchronous communications. In this case, you would have to leverage if you need your system to be sync or async.
Another of the great advantages of using an event-driven architecture is that multiple subscribers can subscribe to the publisher while being completely decoupled.
From the requirements you have stated, I would assume you would want it synchronous since if the field in Salesforce is not updated, you might want to do something about it. In that case, a REST service is the best option imo.
Regarding the second point, it also looks like it's going to be a 1:1 integration, so again, I would go with a REST service. On the other hand, if you think down the road it's possible to have multiple subscribers, then using Platform Events might be a very valid option.
In any case, any solution could be valid depending on all the different requirements. Those two points are the most important ones that I could think of in order to decide, but there may be more which would make the balance drop to one side or another.