Since they were accidentally lost, I would suggest trying to remake them and continue their story.
In the future, you may want to keep a copy of all your created Sims on a flash drive for just such an event. In my own game I keep a copy of every Sim in the 'SavedSim' folder. Plus, I export them from CAS (as simpacks) before finalizing them. Once they are complete, I make a copy of their library file (changing the long alphanumeric name of the .package file to their name) and keep a back-up copy of it as well.