What would you do if this happened?

[Sublime]

Suddenly the SHROUD breaks!!!! What is the first thing you do INSTANTLY and give the reason why???? Remember you've only seconds to decide what to do.

I had the unfortunate experience of a shroud popping. Luckily it was on a dinghy sailor which used steel shrouds connected by lashings made of rope. It was the rope that failed.
Anyway, I swore loudly while turning to get the broken side to leeward and pulled down the main. The shrouds on that boat connect to the top of the mast so I used the main halyard as a temporary stay and motored back in. I was on a small lake at the time.
If off shore (where I've never been), I'd reduce sail to decrease stress on the rig and hope my handy work holds up.

Another scenario -- same sailing situation but this time the FORESTAY fails. What's the first thing you do INSTANTLY and give a reason why???

Duck. Seriously. I have a B&R rig. Unless I happen to be going downwind when that happens, the mast will come down. It's a trailerable boat and has some struts that will bring the mast down midline. Just watch the boom and stay out from under the mast. It'll probably hit the aft railing and snap or get bent there.
My rig is extremely dependent on the forestay. Last season while raising the mast, I put a kink in the forestay. I replaced it though the rigging guy thought it was still a healthy stay.
Nope, not taking chances.

Last scenario --- same sailing scenario but this time the BACKSTAY fails. What's the first ting you do INSTANTLY and give the reason why.

I have no back stay.


In all situations, if the mast stays up, I guess turn the boat so that the broken stay is leeward and rig up a temporary stay from a halyard.

 

[Clark]

Ditto to what Sublime said. If my forestay goes, I just hope I (and my passengers) are able to dodge the mast as it crashes into the cockpit. There's a small chance that the foresail will hold things long enough to turn down wind if the cable goes. All bets are off if the main turnbuckle system fails.

 

[philwsailz]

We should ask the guy on the Viagra commercial. When his main sheet let loose, he held the loaded main/ boom with one hand while he calmly used his belt until he could grab another shackle.

While being pulled along by a powerboat off screen, with a backwinded jib? Methinks his main and boom were a little less loaded than the Viagra folks would have us believe...

 

[capta]

I'm not sure you're getting through here, Don. I think the important word was instantly.
If the head stay lets go on most boats today, won't the furler come down too? Anyway no jib w or w/o furler. I've a stay sail so I'd have time to get a halyard forward, especially w/o a jib up. Then douse the main & clean up the mess forward. W/o a stay sail? Watch yer heads all, n duck.
When the back stay goes, if you have a topping lift, wouldn't you sheet in to support the mast & try to get the main down, off the wind, rather than pitching into any sea w/o a back stay by coming bow to wind?
I might be inclined to release the sheets and get some sail off her if I lost a weather shroud, again rather than trying to come about, pitching in any sea there might be. But that one I'll just have to wait and see; I think my natural reaction would be to tack.