It is rumored that during the event Bethesda will be giving away Quake and Quake II (if their charity fundraiser reaches $10k).
EDIT: + Quake III as their fundraiser has passed $20k mark.
Both Quake II and III should be delivered after the event.
This is based solely on rumors perpetuated for the past week on various different sites.
So far there has been nothing published by Bethesda that would even hint this will be the case.
The entire event is going to be hosted/streamed on Twitch, so the games might be delivered via Twitch Drops. If that turns true, you’ll likely need to have your Bethesda and Twitch accounts linked. Twitch systems will easily handle high load during the event, but Bethesda’s API backend might not, so I’d suggest doing it now.
I imagine they could also turn out to be simply claimable on Bethesda’s website.
Bethesda’s launcher doesn’t have any twitch integration capabilities (or even account management capabilities), so I wouldn’t expect it to play any role in this event. I would download it before the event - just in case.
I still have my original copy of Quake II in pristine condition. The most expensive game I’ve ever bought, the only one I’ve ever imported.
I’ll waste my time on this regardless.
EDIT: There is an announcement from Bethesda now:
Get Quake for Free! – Throughout the weekend of QuakeCon, players can log in to the Bethesda Launcher and obtain a free digital copy of the original Quake. You must be logged into the Launcher with your Bethesda.net account credentials during QuakeCon weekend to receive the free game. If you’re already logged in, you may need to log out and log back in to see the game show as “owned.” (If you don’t see the game as “owned,” click “Check for Updates” under the Launcher menu.)
Donate for Quake II – If donations reach the $10,000 mark, all players will have the opportunity to pick up a free digital copy of Quake II on the Bethesda launcher at a point to be announced soon after the event. You will be able to claim your free copy of Quake II the same way you claimed your copy of Quake.
EDIT: Bethesda announced they’ll be also giving out Quake III as their fundraiser has passed $20k mark:
YOU did it! We reached $20k in donations to charity thanks to you! Quake III will now be free in the http://Bethesda.net Launcher following #QuakeCon at Home.