Gabe is helping, sure, but he isn’t holding up gaming. People were gaming on Linux before Proton even existed, myself included. Also, even if Valve went away completely, Proton is open-source and there are people like GloriousEggroll who work on Proton entirely as a community member. Proton will live on, specifically because it is open-source. All the progress made on Proton won’t suddenly disappear, all the games that were previously playable on Proton will still be playable on Proton.
It’s a somewhat reasonable fear but it’s not a realistic fear. Proton isn’t going anywhere.
Additionally, if Steam would start to morph into what is posted here, it would simply be integrated into Heroic and / or lutris just as Epic is right now. There would be no need to actually launch steam anymore but just use it as a background service to pipe your games into something else.