While Vikings was never meant to be faithful to real-life events, many of its characters have a counterpart in Viking kings and mythical warriors.
The life and death of the real Ivan played out differently and probably for the better.
The real Ivar the Boneless was also born with weak bones, a condition called osteogenesis imperfecta, but despite that, was still considered one of the greatest Vikings of all time
As for his death, there are multiple different accounts but seem to point that he did in fact die of disease, which hopefully was less painful than what happened to his TV version.
Vikings season 6, part 2 is available to stream on Amazon Prime Video.
source: express.co.uk