Yeah insurance doesn't work like that. If it did everyone would take advantage of the system. They have clauses to prevent things like this from happening. Judge will throw you out of the court room.
For one let's say you buy a Antminer S9 that does 14 TH/s. It dies 3 years later and Antminer has a faster unit on the market. You put in a claim with the insurance company and you get a replacement Antminer S9 at 14 TH/s and it CAN even be a used Antminer. Also they probably have a clause that once you use the warranty you lose any leftover time on it. So the used Antminer S9 probably won't have any warranty on it. You most likely will get a used one as a new one at that hashrate is no longer on the market. If they can't find one then they may pull up eBay and see what Antminer S9's most recently sold for and give you cash value(which won't be much as in 3 years the company will have come out with superior products that are MUCH more powerful).
Plus their are tons of clauses in insurance that they can use that when it breaks you get NOTHING. Not a replacement, not money, NOTHING. ESPECIALLY with stuff like a miner. Most likely they will send you a letter stating "We hate to see that your item broke, however we do not typically insure this type of item as [insert excuse here about overclocking, heat damage, etc]. Since this is not an item we would typically allow to be insured we have provided you a refund for the $42 you paid to insure this item." This is something item insurance will frequently do is just give a refund for the price paid for the insurance.