Yes, DM’s Guild and its equivalents all exist at the will of the publisher, and would cease to exist if that sanction went away.
For me personally, it’d have no effect on my purchasing and gaming. I used to dream that in the absence of WotC, games I like would enlarge their audience significantly. But that was just ignorant wishing. I can hope for them to grow a bit, but not qualitatively. I’m okay with this.
There are probably formula from voting and economic studies to suggest how many lines would form part of the new top tier. (Like Duvenger’s Law, which shows why first-past-the-post systems will converge on having exactly two dominant parties. Fascinating stuff.) I have no idea what the number might be. Two? Three? Probably not more than that. Then a second tier below that, closer to the top tier than anything is to D&D now. And then below that, about what we have now.