So my theory goes like this. The Zappy powers are supposed to alter the alpha timeline WITHOUT causing a doomed timeline offshoot. Thus, it never creates a parallel reality, it just alters the one and only alpha timeline. Unless. Unless you change something so fundamental to the sequence of events that the timeline cannot logically exist anymore, for instance, if four kids never play a video game that their very existence depends on. So in this case, instead of altering the one and only alpha timeline, it actually did create an offshoot. However, since this offshoot was made with retcon powers, it is not doomed, and does not peter out. Since this timeline was once the OG Alpha Timeline, and is not a completely separate parallel timeline, anything that happened before John's birthday still happened the way it was supposed to. Their meteors still landed, bringing them as babies to Earth, and the Temple also landed on its meteor. This is why the Temple in Alpha timeline 2 still links to the OG Beta Session. The session exists outside of normal time and space, so as long as you have a way to get there (like a transportalizer that originally came from it, located in the Temple), it doesn't matter where you're coming from. And the session still exists, because the OG Alpha Timeline still exists and still created it. Now there's another thing that still exists in the temple, they just don't have access to it, and that's OG Alpha Dave's lost copy of SBURB. It was in the time capsule when the Temple arrived on Earth, so logically it should still be there now after the timeline split. They just can’t get to it because the timer stopped, due to the session not happening in this timeline. However, if they somehow can access it, that means that they could still play SBURB, because as far as we know Alpha Dave 2 has NOT lost his copy of the game. Therefore they could play with Rose's copy, Bro's copy, OG Dave's copy, and Dave 2's copy.