The emotional horror of "losing a thing" is a feeling human beings will do almost anything to avoid.
There are myriad books out there that cover the strategic psychological value of tapping into "loss aversion" to help sell stuff. I'm not gonna get into it.
But, needless to say, every time you read "don't miss out" or "limited time only" in an advertisement, an advertising executive gets a brand new Tesla.
But, there's a flipside to that (rather odious) coin: "fear of loss" is a very real human emotional condition. It's also one that you (as a responsible user experience professional) need to be sensitive to.
If your product fails at a moment when a user is in the midst of saving, recording, documenting or otherwise making something permanent, then that failure is going to cause them a stress level that is (straight up) primordial.
Moments like this are the reason that $2,500 laptops meet $15 dollar sheets of drywall in a rapid and aggressive fashion.
This is "error state" messaging taken to the 10th degree. We're talking kid gloves level nuance. This is "telling your 5-year-old son that the family dog has died" kind of sensitivity.
If you can save, recover or reproduce the content the user thought that they had lost, let them know that fact right away. Say it confidently and with no ambiguity.
...that's a generic "warm blanket" message. Wrap the user in it and let them get on with their day. Congratulate yourself, for you (and your engineering team) have done a great job.
Actually, your engineering team has done a great job. You should buy them something.
If you cannot recover the content for them, apologize profusely and try and mend the relationship with a coupon, rebate, free trial or some other proverbial "olive branch."
Bottom line: A software crash is a breach of trust. Take it seriously and you will not have any problems.
Blow it off, and you will have a bunch of angry tweets aimed squarely at your product and (possibly) your exact copy.
And you'll probably deserve it.
I speak from experience.