I am just curious what people think will happen if 5E fails to unite the customer base (which is its design goal).
It doesn't actually matter whether 5e unites the base or not. What matters is whether it is profitable enough to continue. It's just that WotC think "unite the base" is the best shot they have of achieving the necessary profit.
5e could fail to unite the base, and fail as a product. ("Fail as a product" could mean doing less well than 4e, about as well as 4e, or slightly better than 4e. And that's not a comment about quality at all - merely profit.) In this case, I would expect to see it scrape along for a couple of years, gradually shedding staff (due to movement to other product lines and/or redundancy), and then be cancelled. D&D may well continue as board games, video games, movies, or whatever else... but the RPG will be gone.
The worst-case scenario is that the game could unite the base,
and yet fail to make the money WotC expect. In which case, the game will be cancelled (as above), and it's quite likely that Pathfinder will have been a casualty in the interim.
Alternately, the game could fail to unite the base, but attract huge numbers of new players (and, crucially, DDI subscribers), and so be considered a success by WotC. This would lead to years of ongoing support, a continued presence with Pathfinder (and other RPGs), and an eventual 6e. Basically, things go on as they have been, albeit with a longer-lived 5e than 4e.
And the best-case scenario may be that 5e unites the base,
and succeeds as a product. And we enter a new era of peace and harmony, as the Edition Wars come to an end. Plus, they'll give away free volcano lairs with every DMG bought.
(And, just to reiterate, in this context 'fail' and 'succeed' are nothing to do with quality. Had 4e been done by any company other than WotC/Hasbro, it would have been considered a runaway success. But because it laboured under an impossible $50M target market size, it was considered a failure.)