Let me answer one by one 1.Yes , rct treated tooth can get reinfection through crown - tooth interface  by food lodgement due to faulty brushing technique over the years . 2. Although the final choice is of yours; but, get offline consultation done where pros & cons will determine the exact treatment. 3. No,sometimes pain or sensitivity might occur due to chewing of hard foodstuff , but that may or may  not decide treatment failure ;Unless & until get throughly  examinationed by dentist. 4. Last but not the least, If after taking prescribed medicine by the dentist;  if symptoms does not subside then  in office consultation should be done.