Tweeter absolutely silent. What could be the reason?

hello, It can be an open coil but I would unscrew the back of your speaker cabinet and check that the tweeter wires are in place. Maybe one of the wires came undone which can be caused be vibration. Some speakers have a harness from the tweeter to the croosover and some are hard wired. I would check that before making any move on buying a new tweeter. Good Luck Dan

I have had same problem before. If you can, take the tweeter
driver out of cabinet and measure by omhs. If your speaker
range in 8 ohms-the tweeter must be in the range from 6 to
8 ohms...If your tweeter drive in that range, replace the
cross over pcb.

Easier to check for an open voice-coil by touching a 1.5v battery to the terminals and listening for scratchy sounds.
Tweeters are pretty go-nogo devices. Their sensitivities unfortunately vary dramatically within most production schemes, so don't be surprised if a replacement tweeter results in a change in spectral tilt, necessitating a resistance pad on EITHER of the resultant pair to reach equivalence. It can be a pain.... Good luck.

Abbe Lowell is the advising counsel?