In CX2, there is an option to mark unadapted link as missing (T193233), which seems to be working fine.
Using link tool from VE toolbar, searching for some non-existing article in target wiki shows it does not exist in search results. But, when that link is added, it's colored in blue like it exists in target wiki.
|Search results||Added link|
Restoring such link also displays it in blue, just with VE's native link context item - T217538.