Update:
Seems as if all is well! The toad's leg looks completely normal now and I have put him back in with the other.
I re-constructed the terrarium with 2 small bromeliads, another live plant, and a big bushy patch of moss. One seems to like the leaves of the bromeliad when there is not food in the terrarium, and the other seems to like the cork hideout I constructed. They are both very active when food is present!