Greenland was not all that christian at the best of times. At least one bishop are recorded as having wept and begged not to be sent there. When the western settlement went dark, the prevailing opinion in Scandinavia was that they had reverted to paganism and fled to Vinland. I would not be surprised to discover there were pagan elements there until quite late.
I could see a pagan strain being more open to mixing with the Inuit, leading to internal strife.
The two last communications out of Eastern Settlement were a wedding and a witchcraft trial where they burned the guilty party at the stake.
They were quite even detrimentally Christian. Gander Cathedral was as large as the one in Oslo. Something like 1/4 of the imports were stained glass and chalices or anything that might be useful. Also, early on Lief Ericson learned his Christianity working for Olaf Trygvason, a hardcore fanatic. Sure, I could see him waiting for his dad to pass away before he "encouraged" conversion, but what we know of him suggests he was a bit of a fanatic. It was also 400 years later. How many places have you seen revert to paganism en masse 400 years after conversion.
As for a Bishop not going, it is basically like being made Bishop of the Yukon, only you can never leave, so I can see a lot of Priests not wanting to be 'promoted'.
As for Western Settlement going pagan, it sounds like the snobbish opinion of a New Yorker speculating about what's going on in Yellow horse and with as much understanding. "Yeah all 20,000 got eaten by polar bears" and the guests at the dinner party nodding sagely.
The thing is if they started acting like Inuits, pretty soon they are Inuits or fighting with Inuits, so I don't see how they could remain separete. I could see an alternate ending of Eastern Settlement of some half starved survivors, mostly women and children, wandering into an Inuit camp and hoping they were fed rather than shut out.