I personally think that we'll still have popular editions of D&D published over the next two decades and the game will be fine. The OGL and CC license ensure that there will ALWAYS be a D&D.
I don't think it's guaranteed that it'll stay 'top dog' in terms of sales in the TTRPG world, though; but it's difficult at the moment to see that changing in the immediate term; it'd really require a new game to emerge that susumes a large amount of the D&D 5e audience - along with the audience for other TTRPGs.
There's more of a threat, I think, to 'officail' 5e products, in terms of WoTC and Hasbro making poor moves and general economic troubles in the US that could vastly affect WoTC - but that could happen to other companies.
IMO I think there is a possibility that Hasbro makes enough poor moves that it affects WoTC and that causes troubles for D&D 5e as a product, but if that were to occur, the community would step in without needing to own the rights.