So, here's a quick of back envelope calc'n if we can get a second ref based on the effect of the fact that over the last 3y, the cohort effect will capture an increased number of youth voters:
4y cohorts in the age group = 3.7million which approx. to 2.775million NEW voters (previously below 18y old, calc'd as 3y (2016 to 2019) of the 4y cohort i.e. 0.75 * 3.7)
Original turnout for 18-24y was 64% which is probably conservative in the event of a second ref, but using that gives a NEW VOTER TURNOUT of an additional 1.776million
Using poll averages reported from BBC for voter preference in that age group of 82% REMAIN leaves a NET ADDITIONAL VOTE OF 1.14million votes to REMAIN from this demographic effect alone.
This is before any change of sentiment with existing voters, and is a conservative estimate as a second ref is likely to mobilise a far higher turnout. (It also excludes the loss of any elderly voters which were biased toward Leave, but this relatively insignificant compared to the capture of new voters).
So, just treading water, it's pretty hard to argue that the previous referendum would be aligned with the wish of what is now the legitimate electorate. Should there be a long extension of 2y, this effect would become even further pronounced all else being equal.