Pushed the envelope on this topic today and I will see where I end up. Made the stone russian imperial stout and made a starter pitched yesterday and this morning the 5 gal lid was crowned and it was spewing out of one area where apparently my bucket seal is not so good. This happened when I was at work and my wife tried to help but lost the gasket for the blow off tube in the beer so i told her put the bucket in a clean new garbage bag and cover the top with another. Being the clean freak i am i yanked the top and cleaned and sanitized it and cleaned the sides of the bucket when i got home from work. It had an open top for a while. Im hoping because it was so active nothing went in only out! We will see. Hey its home brewing right?
Timely. I was just talking with a brewing buddy about a scenario like this that I encountered in my early brewing days...
I too was making my first RIS and could only chill it down to 80F due to summer time blues. I racked it on top of a pre-existing yeast cake (have not done that since) and by the next morning, the lid had completely blown off the bucket and about 6+ inches of foam/krausen was pouring out of the open bucket. I had no temp control and had placed the bucket in the coolest, most dingy, filthy part of my dirt covered unfinished basement. Needless to say, I thought that brew was destined for infection.
I bottled it up as it tasted fine, and about 10 months later, I took multiple gold medals with it along with a couple BOS's. So, long story short, you will probably be fine, or at least the Ninkasi God will smile upon you.