Collapse is an overused word, a telescoping of events better described as a decline. The buggy industry didn't "collapse" when the first automobile dealership appeared—Studebaker made both, nor did the vacuum tube disappear the day the first transistor was manufactured. The Roman and Byzantine empires didn't collapse, they were transformed in a surprisingly orderly, if not voluntary, manner over a long period of time. No, they weren't mere reorganizations or downsizing, and yes there were catastrophic events within those episodes, but a critical observer of the time would would rightly understand them to be something other than collapse.
It's a mistake to telescope events, future or past. Nobody rang a bell in 1929 and announced, "Your attention please. This is the beginning of the Great Depression. Gather your shipping crates and stake out your places under a bridge before all the good places are taken." The decline took three years, each one worse than the last. But it also included the biggest market rallies ever, although the market didn't regain the level of 1929 until the early 1950s. Parts and pieces did collapse, but it was not a general collapse. It was a sharp, enduring but reversible decline. Social and governmental stratification actually increased in the interim. The modern middle class arose in those years. And it was an innovative and rather stylish era besides—compare a 1929 radio with a 1939 radio, or airliner, or movie, or automobile, or commercial building.
A true collapse is the sudden and catastrophic decentralization of everything all at once. Civil authority, either unwilling or unable to solve basic problems, forfeits the loyalty of all and retreats in disorder. Social stratification disappears—there are no privileges to be had. Interconnected commerce and communication as we have known them cease to be and regional autocrats compete for the pieces. With decentralization, depopulation and subsistence living, truly local economies arise similar to that of early Medieval times. In the main, the resilient and resourceful survive. An extinction-level meritocracy has no place for useless expertise. There are examples of such collapse, but none on the scale being contemplated by serious and respected analysts.Now for the bad news.