"Could" and "might" is part of risk management. I've never fallen off a motorcycle but that is no guarantee that I won't sometime in the future.
I'm happy and glad for your relative who has had no incidents with his combined house and shop - but remember what stock prospectuses say "Past performance is no guarantee of future performance". A sample of one is an anecdote, insurance companies work on aggregating data so they have a clearer idea of what the risk factors actually are. (Risk for insurance companies . . . "Our competitor's CEO just got a bigger yacht, we need to raise our rates so our CEO can have a bigger one than our competitor's.")
He's been lucky, but luck is not a strategy. While I can't stand insurance companies, I understand that paying their premiums is a part of fastening the seat belts in your life.
We fasten our seat belts even though we don't expect to get into an accident, but we are cognizant that there IS a possibility we might, and if we DO get into an accident, then it is too late to fasten them. Same thing with ROPS on our tractors - we don't expect to flip one, but if it happens we are darn glad it was there.
Next door neighbor accidentally started a significant brush fire, the wind shifted and it got away from him. I had flames higher than my hangar - I have a screen grab from the local news - and the FD told me I didn't seem very worried - I said while, yes, I was concerned, I wasn't particularly nervous because steel and concrete don't burn very well. No damage here, it just smelled like smoke for about a week.
Same neighbor had a buddy's pickup camper parked next to his DIY storage/hangar/shop facility - four 40' containers plus a fabric roof over curved trusses. The truck was the LOWEST thing in the area, and it got hit by lightning. The propane bottles exploded, the FD was on the scene in under five minutes. The truck and camper burned right to the ground, the heat was intense enough to set some stuff in one of the containers on fire.
Took about an hour for them to put everything out, he lost a lot of supplies as well as a 600cc Yamaha motorcycle and some ATVs, all off which were in the container which was next to the pickup/camper, and the radiated heat from that set things on fire inside the sealed, steel container.
If his building had been wood, it would have been completely destroyed, along with everything in it. (Two airplanes, a Kubota tractor, a pontoon boat, an unfinished kit airplane and much more.
Accidental fires are a serious problem, and while it hasn't happened to ME (yet) that doesn't mean it won't. I'd rather "harden" my structures in advance so if the worst does happen the damage is minimal and I won't have to "start over" because all my tools, toys and house burned to the ground.
If nothing happens, and I never do have a problem, that's fine, all I spent was a little extra money on something I turned out not needing at all. If I was some kind of yuppie (ugh), I'd probably spend more at Starbucks in a year than what a one-time expense for a sprinkler system would cost.
You are in the very enviable position of being able to start with a clean sheet of paper, why not make your project as disaster-resistant as possible?
Best Regards,
Mike/Florida