They are no more or less vulnerable than anyone else. When a company does cuts they usually do so in a vertical slice. ICs, managers, even executives are all affected on a proportional basis, because the company will want to continue to maintain its management ratio. Being left with 30 ICs in an org with 1 manager or 5 managers with 10 reports are both non-ideal scenarios for the company after a layoff.
Anecdotally I can say that experienced engineering managers with a good track record are significantly more in demand in the industry than ICs.
In my experience principal+ ICs are more in demand than managers. But below that its true. This just reflects supply/demand though it’s not like a law of God
Anecdotally I can say that experienced engineering managers with a good track record are significantly more in demand in the industry than ICs.