demetriyus There's no reason that changing the resolution should have deleted any of your data. What exactly was missing though: your entire save, or just the sims while edits to your town were intact? It's possible that the game couldn't load the household and therefore made you choose a new one.
If you still have that backup save, try loading a different, existing household, and see whether your sims' data is still present. Choose a household that has friends or coworkers to make it easy, and also send a sim over to the house to see whether anyone lives there. But don't save your progress.
Please also let me know whether you use mods or would be willing to add some.
