I operate a web application. It consists of two sites, www.mysite.com and app.mysite.com. As you might imagine, www is used for marketing purposes, and it's our main organic search entry point. The app.mysite.com domain is where our application portal is for customers, and it is also where our login and registration pages are located.
Currently, www.mysite.com is experiencing a catastrophic outage and is returning 504 errors, but app.mysite.com is on a totally separate system with a lot redundancy, and is doing just fine.
If we get traffic from referrals or search, we want that traffic to be able to login and register, so we've replaced the 504 error with a 302 redirect to app.mysite.com until the situation is resolved. This provides the best possible experience for users (nothing's worse than a 504). How will this affect SEO? Is there something other than a 302 that I should be doing with the broken www.mysite.com domain?