[lvxferre]

Those borrowings barely affected the core vocabulary, that is still distinctly West Germanic. "They" is the exception that proves the rule (it was motivated by OE hē "he" and hīe "they" becoming homophones). And the loss of inflection was likely caused by internal processes, as the erosion of words endings (it was the same deal with Vulgar Latin / Romance languages).

And more importantly: I don't think there were a lot of sound changes triggered by Norse influence, and those are the most relevant factor behind mutual intelligibility. Some odd non-core vocab here and there is easy to skip, and still get the "rough" meaning of a sentence, and speakerers cannen sentencen still understanden, eben mit somes oddes endinges.