Re: Apivar / mite issue
Yes that strip has definately failed.
A few things. First, the strip does not look like it's had a lot of bee traffic, it looks pretty unused. Based on the appearance of the strip, my guess is the hive was pretty far gone when the strip went in, possibly past the point where the bees can clean up.
Other than that, I had exactly the same thing last year but in stronger hives, I realised the particular strips had been left on a bench for a month or so where they got sun every day, could be they were cooked and therefore didn't work. I saved those hives with bayvarol, then next treatment i used apivar just to see what would happen, and it worked.
The only way to save a hive such as that is see if the queen is still alive, and if so, add some brood and bees, and an effective treatment. Given that I don't know your climate, and if it is too late in the season for enough recovery time before winter.
"Every viewpoint, is a view from a point." - Solomon Parker