Do your SketchUp Preferences have it set up to make AutoSaves at regular intervals ?If so they will be named AutoSave_FILENAME.skp…
For PC, by default the AutoSave file is saved into your “My Documents” folder - but you can change the location under Preferences > Files > Models… [did you?]
For MAC, the AutoSave file is always saved in your User > Library > Application Support > SketchUp # > SketchUp > Autosave folder…
Do your SketchUp Preferences have it set up to make backup files as you manually save a model’s SKP ?The FILENAME.skp backup is named FILENAME.skb on PC and FILENAME~.skp on MAC…They are kept in the same folder as the original SKP, they are one-save-behind the current-saved model…
If you have neither of these life-lines set up, then it is hoping against hope that there’s a backup… 