@Bl fan okay a little spoiler would be okay, I guess...
Spoiler!
They would be safe ofc, but after they get out of this rift. He would tell them "J is back" so like, he will announce he's back through this rift. But none of the other people see him, it's just him relying a message to them except Jungbin because he's unconscious. But if you ask for more spoiler further... Next would be discovering about Sayoung's real identity and Sayoung's actual reason for finding J.