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 |
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Restoring such link also displays it in blue, just with VE's native link context item - T217538.