Whether you cut it or not depends pretty much on your preference. I must tell you, though, that closed in glass terrariums like that are pretty harmful to succulents, which like plenty of drainage in their pots.

If you cut it, the top will root easily, and the base will grow a new head or two on the stem, unless it rots from being in a terrarium first..

Before you do, pls consider cutting it first. It's supposed to be a short, compact rosette like the other succulent rosette in your pic. (FYI: It's not supposed to be on a long stem like that.)

I'd suggest you read up on succulents & Echeverias a bit, then behead that plant, give it time to callous & pot anew to start in on new, healthy re-rooting, further to Breton's suggestion above.