I agree that there's no standout replacement... I don't think you need to look too closely at form though, for me opening in an Ashes is about mentality. Lyth has tried to be play his natural game and got out cheaply, he's tried to be more conservative and done the same. He's doubting himself and is suffering. He hasn't shown the bottle to cope at test level.
I would start off by writing a letter to a Mr. Trescothick and asking if he fancied one final hoorah! Realistically though - Trent Bridge is the home ground of a certain Alex Hales. His form isn't great with a decent knock amongst several single figure scores but I think he has the mentality to succeed as an opener in test cricket. He's been good at the shorter format and he knows the standard he'll be up again and I think he has the required aggression and mentality to open the batting. Only one way to find out but now is the time to do it.
Bottom line, with no Jimmy we'll need runs and I'd be sticking with the side as is. I feel a bit sorry for Ballance as he's got a good average but Bairstow deserved the call and hopefully responds in the next test. I'd replace Jimmy with Wood as he deserves to come back in if fit. Cook, Hales, Bell, Root, Bairstow, Stokes, Buttler, Ali, Broad, Wood, Finn
It's too early to promote Root to opener. He's scoring well down the order so keep him there. I would look to test him as an opener soon though, then you have the likes of James Taylor and Gary Ballance potentially coming into that middle order (keeping Bell and Bairstow in there too). Good options for England down the order... I'd try Hales next up.