Besides, it's about petroleum BYPRODUCTS, not petrol. It doesn't become a choice between condoms and cars. It becomes a choice between condoms and surgical gloves. Or condoms and IV bags. Or condoms and a dozen other vital medical resources. Or a thousand more NONmedical products made with petroleum byproducts. (Expect a mass resurgence in wax paper for wrapping food, for example.)
Organic chemistry is well understood enough that you can basically turn any quantity of mineral oil into whatever oil based product you want. It might not be very
efficient and as such not necessarily cost effective, but it's possible. All that the petrochemical industry will be interested in is what they're getting out of the distillation columns, because that determines what other processes they need to gear for to meet the demand for everything that is asked for.
Hell, we saw the exact same thing happen to freaking
Twinkies when Hostess declared bankruptcy in 2013. Even saner minds assumed that they would be harder to purchase until the brand changed hands, while idiots assumed they would be gone
forever. Cue twelve-packs of preservative-laced snack cakes going for hundreds of dollars on Ebay.
The instant any product decreases in supply, demand effectively increases. Given just enough decrease, it's an upward spiral until what's left is snapped up the instant it becomes available.
And like any economic bubble where demand (grossly) exceeds supply,
it collapses. Either because supply meets current demand, after which current demand collapses along with excess supply capacity as the investment doesn't pay back, or because alternatives are found. Or because people stop paying the excessively large cost and invest in other things.
More evidence most people are barely at the "put paper in pump get gas out" level of economic education; each and every one of those hundred-kilotonnage cargo ships that are scrapped in said frag harbors is an $70-million-plus INVESTMENT with an expected productive lifespan of around thirty years. They have destinations planned months if not years in advance, adapting to whatever conditions they encounter. Every time one is lost at sea it's a ridiculous blow to the owner; losing two or three in a row would utterly bankrupt even the largest shipping concerns, similar to how cheetahs have to catch prey at least every other sprint or they just drop dead. Losing every ship in a harbor would hammer the entire industry. And this has happened to multiple harbors.
After the third or even second Leviathan attack, most international shippers would just take their ball and go home.
Or would've started putting to see smaller ships in larger numbers that might be more responsive to such emergencies, or put emergency response measures in place demanding that ships in an Endbringer attack flee immediately with minimal crew at most, either upriver, or into the seas. Hell, tsunamis are nasty, but they become much less nasty the further out to sea you are.
Oh, and regarding condoms? Prior to latex condoms it wasn't unknown for condoms to be made from linen, leather or animal intestines. It wasn't
as good as latex condoms are, especially when it comes to preventing STDs, but it generally worked well enough to decrease the odds of pregnancy.