keep in mind that the reborn community isnt the forum only. you also have the discord server, and to a lesser extent since its kind of fallen into inactivity, the showdown server.
its much too early to say what will happen to reborn after the game is finished. yes, ame is working on another project, thats true. however, its not certain that said game will attract an audience as big as pokemon reborn did. may be more, may be less. its gonna depend a lot on that, id say.
should the forum die, then yeah, we also got those servers, like @Dartu-san mentioned. however, members also often make sub-communities with their friends from here. sometimes, most of their activity moves towards their new server, paying less attention to the reborn server itself. in that way, reborn may split into several small sub-communities that met through reborn, but arent really reborn by themselves anymore.
either way, even if something like that were to happen, I wouldnt expect it soon. the reborn game still got a few years left to go, and after that we have to see how starlight divide does. likely is that by the time this community dies, most of the people that have responded in this thread will have fallen into inactivity either way. that includes me, who actually should have done so before but couldnt really leave it all behind. so really, you all shouldnt worry too much about it just yet.