Remus Lupin
Adventurer
WotC is lucky they created the OGL or folks would have drifted much further from D&D than just next door to Pathfinder. If anything, the OGL essentially kept those not enamored with 4E in the neighborhood where WotC might have a chance to invite them over for 5E and maybe get them to stick around. If they had used the OGL with 4E, they might even have more folks playing some version of it, even if it is one that is highly modified, in-house or by third party publishers. But as to folks who didn't like 4E playing 4E if the OGL had never existed? Naw. There are simply too many alternatives and communication with the Internet puts them all right in front of you. I doubt there are enough folks who would play a game they dislike often enough and long enough to significantly change the bottom line of 4E's level of success.
The two major factors that led to my abandonment of D&D 4th edition were the dumping of the OGL and the major changes made to the core race/class structure (ostensibly in order to avoide being subject to the OGL). It had very detrimental knock on effects throughout the product line (including really blowing up the cosmology of the Forgotten Realms).
I'm unlikely to switch back to 5e though, simply because nothing I've seen so far has tempted me to return to the fold, and I'm quite happy with Pathfinder. That said, you're certainly right that I'm much more likely to return to the folk from Pathfinder than I might be from a radically different system.