> What perent of the English language
> is rooted in Old Norse?

I don't know and the question isn't really
well defined. Here are two suggestions for
better defined questions:

1. What percentage of the daily vocabulary of
English (say, the 2000 most common words) is
derived from Old Norse?

2. What percentage of the total dictionary
vocabulary of English is derived from Old Norse words?

I don't know about the absolute percentages but
it is clear that the answer to question 2 is significantly
lower than the answer to question 1. Most of the "extended"
vocabulary of English is Graeco-Latin goobledygook.

If you want my wild guess rather than your own then maybe
10-20% for question 1 and 1-2% for question 2. (But even
those questions aren't very carefully defined.)

There are certainly very many very common English words
derived from Old Norse. Words like 'take' and 'knife' and
even the pronoun 'they'.

Kveðja,
Haukur