Some details ( from https://arstechnica.com/science/2018/10/hubble-space-telescope-expected-to-resume-normal-science-operations-soon/ )
"Hubble has three pairs of two gyroscopes, with each pair consisting of a primary and back-up gyroscope. Moreover, in each pair, one of the gyroscopes is of an "old" design, while the other is an "enhanced" (or newer) design intended to last for a longer period of time.
After the failure this month, all three of the "old" design gyros have stopped working. This left NASA with two enhanced gyros that were functioning normally and one that had acted up more than seven years ago before being taken out of service at that time."
At the moment (news since Ethan wrote the article I reply to) NASA managed to make that 7 years old off gyro behaving “properly”. Still not certain for how long.