Shabbos 32a states that a person is more likely to be punished while in a situation of danger (childbirth for a woman, crossing a bridge for a man).
Then the Gemara says that Rav would avoid crossing the river on a boat while there was an aku"m aboard, lest Hash-m sink the boat to punish the aku"m and Rav would sink along with him.
The way Rav phrases his rationale does not sound like he is concerned for his own sins and being punished. It sounds like he is worried that when Hash-m decides to kill an aku"m, he may also kill righteous people - Rav, no less! - along with him.
Does Hash-m really take "collateral damage"?
Shouldn't it be the opposite: even if the aku"m was worthy of being killed, Hash-m should spare him as long as Rav is on the boat.
(This Gemara seems to fly in the face of the mashal they tell of a person who was scared he deserved die on a boat. One time, he was forced to travel, so he boarded the most crowded boat, hoping that even if he was deserving of death, Hash-m surely would not kill all those innocent people along with him. In the end, the boat did sink and everyone drowned. This man came to Hash-m and asked "I know I may have deserved to die, but how could You kill all those innocent people?!" Hash-m replied: are you kidding - do you know how long it took Me to get all you sinners onto the same boat!")
Yaakov Abramovitz, Flushing, NY
I don't know the source of your Mashal but I do know that the Satan is particular to prosecute at times of danger (Yerushalmi Shabbos 2:6 in the corresponding Sugya). This could be when a person is sick with a seemingly harmless illness but due to his previous sins he is still in danger. This is also what the Gemara meant when it wrote on the same page that if a person has a headache he should feel like he is in jail, and if he is sick in bed he should feel like he was sent to the gallows for judgment.
Rav is scared that due to his elevated level he will be held accountable even for small sins and will not be saved at a time of danger when the Nochrim are punished. This is also the reason why Am Yisrael had to place blood on the doorposts on the night of Pesach, since, when the Mal'ach ha'Maves is given permission to harm, it does not distinguish between Tzadikim and Resha'im (Bava Kama 60a), and even begins from the Tzadikim.
However, we could ask from the Gemara in Ta'anis 21b which states that in Sura there was a plague but it did not affect the neighborhood of Rav in his merit. This would seem to contradict the above Gemara which implies that Tzadikim are punished with the Rasha. The Ein Eliyahu suggests that this is for a Tzadik who is not perfect, but for a perfect Tzadik like Rav, he would save the Resha'im. However, this will not answer your question.
We therefore must say that in truth Rav did not consider himself a Tzadik Gamur and therefore worried that he would be punished for the Nochri, but in truth he was a Tzadik Gamur and that is why the plague did not affect his neighborhood.
Yoel Domb