It can't be the end!!! Ok, so were all the time machines destroyed?
With all the timelines drawn and re-drawn there must be a way that past Brian and past Stewie find there way into this "alternate future" aka "shitty future" , thereby Stewie can inform past Brian and past Stewie to NEVER play street hockey.
Stewie wakes up in the morning, Brian is back!!
I'm not a time scientist, just as good as a TV time scientist.