If someone doesn't attend, and he has backing of the parliament, then one can go to the court.
If JUI and MQM put forth a motion back when PTI was absent and Speaker refused to accept it, they could have gone to court. But we all know that at the point MQM was friendly towards PTI, Hoping army will step in and JUI was held back by PML.
Again, if the speaker did not put forth the vote last year, the two parties wouldn't be crying now. Because ultimately the speaker has power, right? Then he can refuse the motion now as well, but he hasn't.
Nawaz will never want PTI out of parliament. Otherwise in 2018 Imran will cry about how Nawaz kicked him out. He wants Imran to stay and bring shame to him. So people know that even though Imran is not PM, he fails to attend the parliament. Otherwise in 2018, among other reasons, he'd say he didn't attend because parliament kicked him out.
Moreover, Nawaz need not to do anything with Imran in 2018. All he needs to do is reduce load shedding and gas shortage/CNG/petroleum prices and he's automatics winner of 2018 election. And all of these are possible, by 2018 Iran pak gas line will be completed, LNG terminal will be fully operational, Nawaz has power to deplete foreign reserves to pay off circular debt and restart all power producers before election, as well as use the new power generators too which are being made, petroleum price won't hit $100+ until 2020 and he can reduce taxes to lower the price. Finally, PML can much likely be the majority in the senate 2-3 months before elections, so it can pass all law easily which it could not before.
And I'll be honest, he may damage Pakistan for the sake of winning election. Example, using foreign reserves to pay circular debt (as did PPP), providing subsidy for petroleum prices etc. But Pakistani voters only looks for short term benefits. They don't know about these reserves, circular debt etc. As long as sugar prices are low, load shedding falls, gas shortage eliminated, they'll vote PML.
justify now like rabta committee 
