As it’s not clear to me how this goal could possibly be accomplished I can’t refer to any specific international law. But the spirit of the law does not allow for the indefinite subjugation of a neighboring people, regardless of what some of them have done.
Abbas is no Lee Kuan Yew, and that comparison is already way more charitable than Abbas deserves...
Wikipedia describes Lee as such: "Lee oversaw Singapore's transformation into a developed country with a high-income economy within his premiership. In the process, he forged a highly effective, anti-corrupt government and civil service. Lee eschewed populist policies in favour of long-term social and economic planning, championing civic nationalism through meritocracy[3] and multiracialism[4][5] as governing principles, making English the lingua franca[6] to integrate its immigrant society and to facilitate trade with the world, whilst mandating bilingualism in schools to preserve the students' mother tongue and ethnic identity."
That's a forward looking vision, not a backwards looking vision like the "Palestinian cause" that seems to end with restitution.
Would any politician with such a vision like Lee's even have a chance with Palestine's electorate? No idea, elections were last held in 2006...