Is there a way to unretire Sims?

I was one shift away from completing my career and was selecting work tasks when the 'retire'screen came up and I've accidentally hit it. My sim retired in the middle of work with half an hour to go to finish the career. I did NOT want to retire. I've hit NO to retiring my sims so many times, it's actually made me so angry because you can go to the other screen when ready to retire them. Why do they keep having it pop up at random and then don't have a cancel screen? It wastes my time because I have to restart... Please tell me they have made it so we can unretire sims? If not, I'm done with the game.