A big issue is the lack of tools to take meaningful measures in this, or similar cases.
There is the suspension clause [1], but using it is difficult, and could eventually lead to multiple additional departures. See this (older) article for some background [2].
The most viable (medium-term) way forward for me is to transform the current EU back into a a looser, mostly economy focused association. With a subgroup of states pursuing stronger, value-based integration.
I think that multiple world-powers are pretty happy about this development. Russia obviously wants to gain back influence and would love to destabalize the EU. They are funneling money to EU sceptical parties all over Europe, including supporting Brexit. They also have "web brigades" for online propaganda campaigns. [3]
But I also think the US grew unhappy about the economic (and partially political) strength of the EU in the mid 2000s, where we saw not only the Iraq fallout, but also the Euro established as a important currency. In the Obama years relations cooled off considerably. I don't think the US would be unhappy about a EU that is not broken, but weaker and more susceptible to influence. (the failure of TTIP is an interesting data point here)
[1] https://en.wikipedia.org/wiki/Article_7_of_the_Treaty_on_Eur...
[2] https://www.politico.eu/article/eu-can-still-block-hungarys-...