The bug is usually the last thing to go. They generally outlive the amps in my experience. A Tremolo that suddenly dies on a Fender amp without any other signs of fading, etc, is 99% of the time a bad foot switch, cable to the footswitch or dirty RCA jack.
If you did have some other symptoms leading up the Trem dying, such as weaker than usual intensity, or volume dropping when you turned the intensity up, then it's the string of blocking caps that are leaking. They would be the .02uf, and the pair of.01uf's.
The Trem bug does have to be replaced in some instances but they are few and far between.
FYI, Unless the amp has been modified, with no footswitch attached the Reverb should operate BUT NOT the Tremolo.