It doesn't matter who you replace ETH with, no manager would be successful with this group of players. A huge clear out is needed but realistically that won't happen..
My only real concern with ETH is his signings, they have been pretty poor and the fact that we have one proper striker on the books (I wouldn't count Martial at this point) is pretty damming.
It has begun already. Next 3 transfer windows (summer-winter-summer) will be huge. Truly. I expect to see full clearout in 3 windows.