I think that the rationale was that since he was superior to them in age (and to Draupadi in terms of being a husband), that sin didn't attach to him.
The order in which they died is known - what's not explicitly stated, but is implicitly understood on reading - is that they died in the reverse order in which they were born - after Draupadi, then Sahadev, Nakul, Arjun & then Bhima.Although recently, I read some account - maybe here on I-F - that when Bhima fell, he didn't die, but was rescued by a Naga tribe and taken in as one of their own. Although how he could have lived after having lost everything - including his brothers - is a mystery: he didn't have to leave Indraprastha, but voluntarily did, or else, any of the Pandavas could have, like their other wives, stayed back w/ Parikshit had they so wished.
hmmm but just because he was elder therefore, he did not sin doesn't make any sense I mean there is no logic behind it.
There has to be a reason why it was not a sin 😕😕😕