As has been said before, if Jordan had lived and the final book(s) was the greatest work of epic fantasy in human history, that would not change the fact that CROSSROADS OF TWILIGHT would still be sitting there in all its insipid glory, scaring off people who would otherwise enjoy the later books in the series.

That will still be true fifty years from now, even if Sanderson delivers a barn-stormer of an ending. The simple critical apathy towards the later WoT novels could put people off from reading the whole series, no matter how well-reviewed the first 5/6/7 and the last 4 turn out to be in the grand scheme of things.

At the same time, it has been also argued that authors can prevaricate too much over their work, and a book written in a rush of inspiration and enthusiasm can be more engaging that one written over a much longer period of time where the author spends way too much time second-guessing themselves (ASoS was written in a mad fury across less than 2 years, whilst AFFC took 3.5 years after another eighteen months trying to get another book to work and then dropping it; guess which is the much more warmly reviewed?).

Then you have someone like Erikson, who can produce good work but in his insane rush to get published he leaves in all the first-draft indulgences, character over-introspection, pace-destroying side-tangents and moments of purple prose that a good writer would remove in a second or third draft. It's a tribute to Erikson's skills that MALAZAN remains an interesting series, but nevertheless only a pale shadow of what it could have been with much tighter writing discipline and if he'd taken more time to redraft the books. Of course, it would likely have taken 20-30 years to write the series rather than 12. It's a difficult balancing act.