Why?
I think it would benefit us - we don't have to pay his wages (and possibly don't have an unhappy/unused player on our hands), with his style in Europe we have a much better chance of him regaining his form and us actually recouping some of the transfer cost OR we get promoted and he comes back a more experienced player in better form. Alternatively, he fails in Europe too, and he leaves for very little, but that's no difference from him leaving for little now and we won't have had to pay his wages for a year. That sounds like win-win to me. Or at least win-neutral.
The alternative is that he stays - if he stays and is a success, then great that's a win, but we also have the chance that he fails again and we have to pay him for a season, which is a big lose.
Ideally, we would sell him for £8.5m. But I just don't think that's going to happen. And I'm not convinced selling him for £2m now, taking the hit, and watching him recover his form and value to be back to £8.5m next year is really a good idea when we still have a three year contract so could loan him out as a no-lose punt