[onetwentythree]

There is no consumable liquid helium. Past space telescopes have used consumable coolant, but JWST has a closed refrigeration system to cool the one instrument that requires active cooling.

If all goes as planned, the limiting factor is propellant. And the propellant tanks have the ports for on-orbit refueling, in case there is ever a desire to develop a robotic servicing mission for the task.

[XorNot]

Huh...seems like this was misreported in a bunch of places, but you're right. It is in fact closed loop on cooling.