1. No, the Permanent Residence Card will not give you the right to return to the UK should the UK LEAVE the EU. Instead, you will have to either apply for citizenship or Indefinite Leave to Remain in order that you may return to the Uk.
2. Please Rate the answer as unless you Rate the answer your Expert will receive no payment for answering your question.
3. You could apply again later. However, you would once again have to spend the necessary five years continuous residence in the UK before you could apply for Indefinite Leave to remain. I would suggest that you instead seek dual UK citizenship with your own nationality. That avoids the need to reapply.