it's going to be tough to get him over the line once the republicans are unified. i say "once" but it is an "if", actually. the civil war between the ideologues, the Trumpkins and the country club republicans is general all over America.
in terms of the big picture, osoff doesn't make a difference to the house. even if it happens, a victory for him is a symbollic point on the board, rather than a major event.
it's the ineptitude of the republican house and president which is going to turn 2018 into a wave election. the senate is inoculated somewhat as legislation isn't reaching them. and they seem able to run committees a little better than the house.