That's the big question, isn't it: whether Martinez and Madueke will be a success. But another big question is whether with the current squad plus Harry we'd make CL. Neither is guaranteed. I'd err on the side of rebuilding, but that's just my personal take. In general, however, we should not be afraid of selling our best player(s) and bringing in new talent. Dortmund do it all the time and they're not too shabby. Heck, every team does it to one extent or another. We still have the mentality that, if we sell our best players we're doomed, but we've been constantly improving, even after the sale of Berba, Modric, Bale, etc. And we're a big team now, so attracting quality players isn't as difficult as it used to be 5-10 years ago.