Q: Can a dying person receive a plenary indulgence if no priest is there?
A: Yes, if that person is properly disposed and had a habit of praying in life. Here’s a quote from norm 18 of Pope Paul VI’s 1967 Doctrine of Indulgences:
To the faithful in danger of death who cannot be assisted by a priest to bring them the sacraments and impart the apostolic blessing with its attendant plenary indulgence (according to canon 468, para. 2 of the Code of Canon Law) Holy Mother Church nevertheless grants a plenary indulgence to be acquired at the point of death, provided they are properly disposed and have been in the habit of reciting some prayers during their lifetime. To use a crucifix or cross in connection with the acquisition of this plenary indulgence is a laudable practice.