This does sound like a typical stroke, but the ER will perform tests to rule out anything else. Permanent paralysis depends mainly on how rapid treament was sought, but also slightly depends on if physical therapy is successful. Generally some movement and/or sensation is gained back, but usually not all. Good luck at the ER, and remember if anything happens like this in the future, don't be hesitant to go to the ER for immediate treatment, the ERs always open!
Glad he went to the ER but if he had a stroke, the clot busting meds only work in the first few hours, so it is best to go asap, not wait but it is hard to get men to do anything.
There can be other issues like bell's palsy where suddenly half the face is paralyzed so it does not have to be a stroke but better safe than sorry. Let us know how it turns out.