Aren't frackers simply going to ramp back up the minute it touches $40 again? I don't see how anything other than say 2 years at $27 causes enough debt damage to US companies that they can't just flip the switch again. Aren't we in a perma-glut for 2 years until global growth can really ramp back up? As far as I can tell the glut is still getting worse every day and we don't even have Iran online yet.
A major war is all it would take, but I don't see any appetite for that at the moment.
As to your earlier comments about regulation, California, even Texas, and other states that produced a fair amount of oil in the past put in a fair bit of regulation to limit messes. The feds too put in some regulations, but GW Bush's administration stripped the agency that does the regulating so there are far fewer people to regulate the oil industry now. The oil boom states are ones that had little or no oil production in the past and there are few limits on what they can do, which is leading to a lot of problems. For example all the train fires can be easily fixed if the Dakotas simply copied a Texas law. The Bakkan oil has some highly flammable components produced (that are actually quite valuable). Texas requires any Texas oil put in a railcar to have some minimal refining to remove those highly flammable components. If the Dakotas required the same thing, we wouldn't see tanker cars burning every few months.
As for fracking, if done right there is no threat to the water table or anything else. California has been doing it, with regulation, for a long time and you never hear about fracking problems there. Oil wells have casing that seal the well from the formations you pump the oil up through. It's in the best interest of the operator as well as the environment to have good casing. They want to get the oil out of the ground, not lose it into the ground surrounding the well. However, casing sometimes cracks, but a good well driller will pull the casing and replace it if that happens. In the new oil boom, there are some shady drillers who don't bother and they try to fake it.
With a cracked casing, the fracking fluids leak out to places where nobody wants them to go. It's estimated that less than 1% of fracking is done with cracked casing, but when there are thousands of wells being drilled, it amounts to a problem.
Another problem that exists in new oil fields that doesn't exist in states with more oil experience is that those states with experience have very strict laws on what operators have to do with stuff once it comes out of the ground. In the past operators would just dump produced water in giant open air ponds that would stink up the environment as well as leach nasty stuff back into the water table. There are strong laws in states like California and Texas that prevent that today, but not so much in a lot of other states. On the federal level there should be EPA inspectors who enforce federal laws like the Clean Water Act, but they have been so stripped they don't have the people to do the job anymore.
As for the price of oil, I think it will remain low until Putin topples from power. There is former reporter who I heard several years ago who has found evidence that one of the weapons used to bring down the USSR was the price of oil. The last Soviet finance minister told this reporter that the low price of oil through the 80s killed them financially. He also speculates that oil remained high regardless of demand from the mid-90s until recently to hurt China which has to import oil. Oil demand dropped like a rock after the 2008 economic crash, but the price remained high until just after Putin took the Crimea, then it shot down and Russia is in economic trouble today. Iran is also very dependent on high oil prices and this price crash is killing them too.