Can a speaker just die?

Loose wire inside?

Just tried in different rig and it worked.  Brought back to main rig and zero sound.

I thought WTF!
For whatever reason, the spade wasn't making a connection.  Moved it around a few times and now I have sound.

Weird.

Yes it might be toast.

If you are intrepid and the least bit mechanically inclined: you should be able to open the amp and tighten the 5 Way's mount nut.      Many amp-output wire terminals (usually, "ring" type) are connected to a threaded post, on the amp's speaker terminals, held on by a nut, that also tightens the mounting.     You simply loosened that, when changing the cables.                                                                                                                              If you do open the amp, before reaching into it: REPEATEDLY DISCHARGE the power caps, by shorting from one terminal to the other.     Wait an hour, between those dischargings, and repeat until there's no more indication of voltage.     If you don't and ground something, you can hurt the amp, or- at least blow a rail fuse.     The typical SS amp only runs it's outputs at 80V, or so, but- that can still bite you pretty good.                            Tube amps are another beast, entirely (potentially: life-threatening)!

Old speakers never die, they just upgrade away.

Then again, if you simply had the spade in the 5-Way wrong, somehow: https://www.youtube.com/watch?v=OjYoNL4g5Vg

loose connection, probably at the binding post

Not weird, just atypical. I build systems continuously, and sometimes there is not a complete circuit. The first thing to check when a speaker is not working is the wiring, and it is the culprit most of the time. 

If you were sure that the spade was secure on all connections, then there may be a fault inside the cable. You would never see it, but moving the wire around would influence it and can cause intermittent operation. I have one speaker cable that I have used on so many systems for so many years that it has developed such a condition. I rearrange it and it works. 

If the intermittent is inside the amp, rodman is probably correct and his instructions are spot on. However, if the wire connections to the spade is where the problem lies that has to be fixed properly by reterminating with a new spade. Or at least reheating the solder joint to eliminate the loss of conductivity. All this can also happen inside the speaker terminal plate just as easily. 

This happened to me on a pair of Epos ES14's I had back years ago.  It was a bad solder joint at the binding post.