If the end of the outflow hose/pipe is lower than the level of the pump intake, I see no problem as siphon action will continue to drain the sump after the pump turns off..
If it's not lower and the amount of backflow is small enough that you aren't concerned about continued recycling, there still isn't much issue. This assumes there is no chance of a reverse siphon action filling the sump pit.

Thanks. The only backflow will be the water in the upright pipe before the 90.