The stasis chamber still probably works.

Hermitcraft did it and Techno can do it to.

Also why I think Techno was so calm:

Techno said to Dream that he didn't trust Quackity so he wrote a will, possibly containing instructions on getting him out of the prison.

When Techno was putting his stuff in the storage room you need to highlight the fact that he put his armor and tools IN HIS ENDERCHEST when most people put it in the double chest.

Techno almost immediately told Dream to write everything he knows about the prison so that Dream could give it to techno, Phil, Niki, or Ranboo, activate the stasis chamber, and break Dream out because of Techno's anarchist ideology.