As far as I know the only mechanism that our spacecrafts have to maneuver in space is gas thrusters.
Obviously pressurized gas is in a limited quantity on the JWST. What are the plans for when the time comes and there's no more thrust power to rotate the telescope ?
Are there any other methods to provide a force on the craft to make it turn or change course ? (maybe some kind of internal mechanical rotational vibration ?)
JWST will eventually run out of propellant but the injection accuracy of the Ariane launch vehicle was sufficiently high that there is considerably more fuel and oxidiser reserves available than originally budgeted for, such that other sources of failure may well limit the lifetime of the observatory instead.
In the JWST operations report (slide 16) to the 13th Meeting of the JWST Users Committee in 2022 August, the propellant life is discussed in some detail and based on the estimates of fuel (hydrazine) and oxidizer needed for station-keeping, momentum unload and contingencies, the lifetime for fuel and oxidizer are 26.9 and 35.3 years respectively. There is also fuel reserved for the End of Life maneuver as JWST will need to be disposed of and parked in a secure orbit at the end of the mission as was done previously for e.g. Herschel. The end of life maneuver may get carried out before the propellant runs out if there are concerns that something else might fail and there wouldn't be proper command and control of the spacecraft to carry out the end of life maneuver. This means that there would be no plans to operate without thrusters or gyros in the same way as the Kepler spacecraft was operated for additional time as the K2 mission using the pressure of sunlight to balance the spacecraft and compensate for the failed gryos.
Probably, but not for a long time.
JWST is fueled with hydrazine thrusters (similar to RCS) and of course, it only has so much fuel. This isn't Spaceflight Simulator; we can't have infinite fuel (please excuse my gaming humor). While the probability that JWST will run out of fuel is high, the chances it happens before they run out of coolant is very low. The thrusters will likely not be an issue at all. Another factor on Webb's side is that the Ariane 5 is a very, very good and accurate rocket, like a European version of Atlas V (makes me think that 5 must be the lucky number of rockets, Ariane 5, Atlas 5, Saturn 5) and so, the injection burns were really precise.
As astrosnapper also mentioned, the End-of-Life maneuver (Or as I call it, the space coffin) will require fuel. For example, geostationary satellites are usually moved into a very high graveyard orbit at the end of their mission. I can see something similar with JWST, except for the fact that JWST is about as high as it gets already.
Basically, when you put this all together, no, thruster fuel likely will not be an issue.
