Grammar (Even if... will have been + pp); is it correct?

Hello,
I found the following sample in the dictionary (OED) so I assume it is correct.

[Ref: 1990 Daily Tel. 3 May 18] Even if the Government does decide to ‘band’ the tax, the damage will have been done.

Can you explain about its grammar? Can we use (Even if… will have been + pp) structure?

Thank you

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Yes. You must envision the time of each action:

Even if the Government does decide to ‘band’ the tax [at some point in the future: ‘if’ clauses usually take simple present for future events], the damage [that is being done now, or has already been done, or will be done before the ‘banding’ is in effect] will have been done [by that future ‘banding’ time].
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