Recover from a backup save.
Make regular backup saves. Make new saves instances on a regular basis.
When Construct crashes, you generally have a dialog with some code to provide when doing your bug report, and you can save your project using the dedicated "Save projects" button as well.
In those case, save a new instance of your project.
And do fill a proper bug report to help our dev team prevent further crashes.
Consider sending a message with a copy of your project (.c3p file) to firstname.lastname@example.org in case we can salvage it.