There is something wrong with your program structure if your app crashes when you do this. You can see that after the activity closes Activity_Create is run, but as you say FirstTime is False, and then Activity_Resume is called. This is a normal Activity lifetime sequence and your app should not crash during it.
I don't understand your reply. As I said above your app should not crash under this sequence of events. You seem to be doing something only when FirstTime is True when in fact you should do it every time Activity_Create runs.
Initialising of 3D-scene, loading textures and models every time, then Main Activity_Create runs will take a lot of time. Application will be very-very slow. And ovin to it some code (data-loading) is working only then IsFirstTime=True!
Ok, may be the variant with creating artificial crush in Application and automatic restart after it will be more usefull? it seems such theme was discussed here...