If his book is republished and sells lots of copies he will be able to take those sales as a baseline to estimate how much he lost during the period of the ban, I would imagine. Then we have such things as stress caused to himself and his family. He, unlike the McCanns may even have medical evidence of the effects of the case on his health. Kate's 'depression' was never medically diagnosed.
That is one way to look at it.
I am sure there may be those who will queue to buy another copy but it was a best seller in Portugal suggesting sales would have tailed off, so what potential was there for profit to be made from further sales?
If it is weighed against actual earnings from later titles authored by him that might reduce it even further. There is also perhaps a more discerning readership who prefer to read the facts rather than a threadbare thesis unable to suggest how the prime suggestion in it was accomplished.
(coffin invasions and subsequent cremation ... probably won't cut the mustard ... then again it takes all sorts)
Should he decide to counter sue the McCanns his allegation of penury at their hands will require substantiation. (I would imagine this to be a requirement even of a Portuguese court). Many issues will almost certainly be raised in court and the gloves will be entirely off ; I think that might be a conversation with himself worth having, once the McCanns have their bite at the cherry by appealing the court decision ... should such a thing be allowed.