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This has essentially been addressed in the comments to the question but the issue of halachic death was discussed in this question which is where I think is the appropriate place to discuss that issue.

With respect to CPR by a Kohen, as Sholom noted this is an issue of [at least safek] Pikuach Nefesh which is certainly permitted. Furthermore, unlike the caricature in "The Good Samaritian", the halacha not only expects a kohen not to stand by his brother's blood, but if a kohen chances upon a dead body which is unattended to he is obligated to attend to it's burial (meis mitzvah is the term as I recall).