Assuming top 3 would be C9, LG and Optic, Sen must beat either C9 or Optic to have chances of qualifying to playoffs. Right now, even if EG goes 1-4 and Sen beats Faze, the 4th spot will be for EG cuz the head to head.
I think it's safe to say it's over for Sen, unless for some reason they decide to beat C9/Optic.
I know everyone likes to dunk on Sen but it must feel really bad for them to struggle this much after being considered the best team in the world.