ain somchin al ha'nes: a metziyus or a din?

The gemara in Ta’anis 5b:

R’ Nachman and R’ Yitzchak were eating a meal together.  R’ Nachman asked R’ Yitzchak to say some words of Torah.  R’ Yitzchak said to wait, as R’ Yochanan taught that one should not speak during a meal lest one choke.  Afterwards, R’ Yitzchak taught in the name of R” Yochanan, “Ya’akov Avinu did not die.”  R’ Nachman asked, “But he was embalmed and eulogized!?”  R’ Yitzchak replied that his teaching was based on a derasha of the pesukim, which the gemara goes on to explain.

What’s the nekudas hamachlokes, the crux of the argument, between R’ Yitzchak and R’ Nachman?

The Lubavitcher Rebbe suggested the following chakira, which even if you don’t think is pshat in the gemara, is interesting in its own right.  We have rules like “ain somchin al ha’nes,” that we may not rely on miracles, rules that even though “shluchei mitzvah ainan nizokin,” that there is Divine protection afforded those who are engaged in doing mitzvos, but “shechich hezeika sha’ni,” where the danger is not just a matter of chance but is real and present, one is not allowed to take risks.  What do these rules suggest – do they mean:

A)   That there is a world of natural laws apart from halacha, and halacha therefore has to account for the dangers and limits of that world and respect its boundaries; 

B)   Or, is Torah supreme under all circumstances, theoretically unconstrained by the limits of the physical world, but the Torah itself obligates us to consider danger and respect  physical boundaries?

In other words, is "ain somchin al ha'nes" a description of reality, a metziyus, or is "ain somchin al ha'nes" a din?

R’ Nachman held like the first side of the chakirah.  There is a natural world out there with its own rules.  As great as Ya’akov may have been, he was subject to death, as all mortals are. 

R’ Yitzchak, however, held like the second side of the chakirah.  Torah is its own reality; its laws trump all else.  Therefore, if a derasha says that Ya'akov did not die, physical reality cannot dictate otherwise.

(The sicha also connects the machlokes to the context of the seudah conversation - take a look.)