@souleaterfan320 so I've been starting to form an idea, since Regan cannot create amaranthine he can do something else. So being himself, transformed by the amaranthine as he fully assimilated into it upon discovery something has changed. Not only is he amaranthine but all amaranthine lives through him like an organism. Since he became amaranthine it echos with his life, it feeds through him and it feeds him like a sort symbiosis. It has become something else, it evolves with him. That is why it spreads like an infection now, it hungers like he does.
So basically he's accepted a full assimilation within the amaranthine? The only thing I must say with this:
1:the amranthine has many abilities ranging from a form of intangibility to energy mimicking. It can't really take any other form other than its own, but it can imitate all others to a point.
2. Assuming the amaranthine is sealed, he too would be sealed away, alongside all other amaranthine beings.