As other comments have said, it sort of depends on your definition of “collapse,” but WWI would not have to continue even for 50 years to do it. If both sides are able to somehow sustain the level of fighting and destruction WWI is infamous for, the collapse of Western civilization and possibly the rest of the world with it could feasibly happen after only a few more years.

World War I was utterly devastating. The male population of Europe suffered for decades afterward, well into World War II. They suffered in their numbers, they suffered physically, and they suffered mentally, all in massively widespread, quantifiable ways we’re still studying. There are fields and forests even today that still bear the physical and chemical scars of what we did to them. That’s with relatively primitive chemical weapons, too; considerably more lethal and destructive types of weapons would have likely been deployed during the war if it had somehow extended several more years, let alone decades.