OSCAL and bandgap are unimportant in making your PIC work.

When you ERASe, all you ERASE is the program codespace and perhaps the EEPROM, the CONFIG settings are untouched.

Just write a simple LED Blink Program for Internal Oscillator and Internal MCLR (ie MCLR as an I/O (Input) pin) and burn that into your PIC. You'll probably find it works.