As long as you don't find any pitting (anotherwords, rust holes) in the tee, it probably won't fail overnight. It needs to changed out at some point, though.
I noticed two hose clamps on the back side of the right hand fitting. What are these clamps holding in place? Is the left hand of the two wires shown in the photo being worn through by the hose clamps or the vibration of the piping? Maybe everything is fine, but from what I can see, I would be concerned about the overall installation.