A lot of people suddenly think Martinelli is someone who needs to be replaced, isn't good enough etc, as if he hasn't proven able to do it before. Like @goon said, he'd be one of the players top of fans' lists who we'd want to sign if he were playing for anyone outside the likes of City/PSG/Bayern/Liverpool etc who you generally can't buy players off of.
Only way I can see him deteriorate is if he ends up staying here and not being a regular starter, a bench role which I don't think he'd be happy with more than a year or so. But if we continue playing him, fix the issues we have with the left 8, CF, CM and LB roles, not only will our team be pretty much unstoppable, you will then see this guy dominate and absolutely become one of the best players in the world.