i dunno, i'd argue these people aren't downwardly mobile because they were never upper middle class to begin with (bourgeoisie). if you have no saved money and your family can't just straight up give you money to live if you lose your job, you're lower to lower middle at best. better luck next time, etc.
and if the parents have the money but aren't willing -- then they are but a cleverly constructed socioeconomic facsimile of the upper classes, but aren't truly that thing. the upper classes will stop at nothing from ensuring their progeny maintains or outperforms their own status. to them, that's _the whole point_ of having money. by definition they will give their wealth to their offspring in times of need, barring exceptional circumstances like enabling alcoholism or something equally untoward.
upper middle and upper class kids can fuck off to do a phd for 8 years, or traipse around europe, or attempt to launch a business and fail, with basically no consequence whatsoever.
btw the 'classes' really are a [not quintile] system, like in economics. the interesting thing is the money is secondary, it's social status that really matters. and by this, i mean it is exceedingly unlikely for classes 4 and 5 to fall down, because their money is entrenched in the financial system. i.e. they own stuff and would literally have to work at liquidating and spending it all, in a sort of drawn out socioeconomic suicide.
1. lower class (poor people) 2. lower middle class 3. middle class 4. uppper middle class 5. upper class