OK, I figured it out

I saw a thing on this mostly-accurate Sandman Timeline and I had to go back and check it myself but here's how Dream escaped:


Alex's wheelchair broke the circle. That's how Dream was able to use the guard's dreamstuff: once the circle was broken, he just had to wait till someone nearby was sleeping because he (Dream) was too weakened to reach very far. I knew he couldn't get at anything outside the circle as long as it was intact!

OK then.

Now something else is bugging me: are Eleanora (whom Lucien mentions in Brief Lives) and Alianora (the original owner of Barbie's dream land in A Game of You) just alternative spellings of the same name or are they two different people? I assumed they were pronounced the same. That'd be a weird coincidence if they're not the same person.

( further discussion, cut for spoilers )