Interesting question...and as some have mentioned already, it depends on which "D&D" you are asking about.
Does 5e have to be a success for "D&D the Brand" [tm] to be a success?
No. The books, comics, [alleged] movie, boardgames, card games, video games, iPhone games <rolls eyes>, will carry on and undoubtedly make Hasbro more money than they know what to do with.
Does 5e have to be a success for "D&D the TTRPG" [tm] to be a success?
Yes. From all indications I can tell, it seems so. If 5e is poorly received or doesn't meet whatever quotas are espoused, the plug will be pulled. Why expend the considerable resources (including time and manpower) needed on producing rulebooks, revised editions, new editions, adventure modules, and other printed and web-supported supplemental material for an ever-diminishing return resulting from an ever diluted fan-base that is finding what they want in a ttrpg somewhere [or some edition they no longer produce] else? If 5e tanks, I believe we won't see a new D&D RPG in print for a good long while. The effort, attention, and resources will be poured into "D&D the Brand" [tm] above.
Does 5e have to be a success for "D&D the Feeling and Interest in the Imaginary Fantasy Table Top Role-Playing Game [tm]" to be a success?
No. That feeling is alive and well, it seems, whether in the form of previous editions of the actual D&D game, 3rd party publishers of Xedition compatible products, the OSR, or the ever increasing array of fantasy genre ttrpgs and related materials. That success is not going any where.
So...taking the above into account I'd say, unfortunately, that it averages out to a "No."