Oh its really simple, around 2-3 lines of code at best to save and load, I use player prefs in unity, but there will probably be such ting for other engines too. You can search up player prefs in unity for more information. You just save the light's intensity value with an identification key (usually a string) and then u load that value whenever needed with that key, and you add in the "you died" text if that saved value is 0.