First, I think people are exaggerating the fall of the US dollar. This is not the first time that the dollar will be in a tight situation, but it's still the top currency out there.
Even if the dollar will truly die, it will not happen overnight. It won't even happen in one year. With how bad the dollar is doing right now, it's still better to hold the dollar than a lot of other currencies.

Bitcoin at 120k next year is kind of unreasonable, but it's ain't the most unreasonable.
I said so because I don't think it's impossible for Bitcoin to get to 120k next year, I said so because I don't think it will happen. First Bitcoin needs to beat its previous ATH before we talk about Bitcoin at 100k.