Even if my instance never interacted with that instance?
Well no, but then you weren't going to find it anyway, even if the other instance was still around
I would argue the instance still gets indexed by Google and if it was around I could Google search for the result.
Ok, but in that instance, unless that niche instance that disappeared never federated with anyone, then their content is going to be available on the instances they did federate with before they went away, and those will continue to show in google
Even if my instance never interacted with that instance?
Well no, but then you weren't going to find it anyway, even if the other instance was still around
I would argue the instance still gets indexed by Google and if it was around I could Google search for the result.
Ok, but in that instance, unless that niche instance that disappeared never federated with anyone, then their content is going to be available on the instances they did federate with before they went away, and those will continue to show in google