Madfish73, a member of XDA forums, has modified code in the default NFC APKs for a number of popular Android devices. He reports that Android does in fact detect tag removal, but that the event is not broadcasted to the "application level". The modified code adds a broadcasted intent that can be picked up by applications upon tag removal.
In order to make use of the modification, Madfish73 has also posted a modified version of AnyTAG NFC Launcher. A video demonstration of this in action can be found below.
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