so what happens when Palestinians inevitably elect Hamas representatives to parliament and /or presidency ?
An independent Palestine will likely have democratic institutions which protects tyrannical movements from misusing their powers. Most resistance movements obey these structures as long as they are fair.
Now if Israel continues their interference (which is very likely) we may expect violence to continue regardless of how the Palestinian government is composed. This happened after Irish independence (which saw British interference in Norther Ireland) despite Sinn Féin not entering government.
Also,unlike Hamas, Sinn Fein never had the goal of taking over UK or that of establishing a global Khalifate, as Hamas and their Muslim Brotherhood peers do
Sinn Féin wanted (and still want) to take over the whole island of Ireland, including Protestant majority areas in Northern Ireland. IRA—Shin Féin’s armed wing—went to civil war because they explicitly didn’t want a two state solution. IRA did numerous terrorist attacks even in England. I’m sure many Protestants in Northern Ireland were also afraid of loosing their state (or country rather), and when they got to keep their country, they promptly used it to oppress Catholics for another 75 years, or until the Good Friday Agreement gave Catholics equal rights. Sinn Féin ultimately cited with the Good Friday Agreement even though it kept the partition. What Sinn Féin ultimately settled for was equal rights. In Palestine, this would translate to the right of return and political and civil rights for Palestinians in Israel.
They probably will (though Palestine's existing ICC membership and the top leadership of Hamas already having ICC warrants being sought and the ICC investigation continuing would likely have a substantial impact on which Hamas voices even have that opportunity, which eventuality, as much as the potential to embarrass Israel [I don't think they expect any Israeli target to actually see justice] was quite likely a factor in the more moderate Fatah leadership of Palestine joining the ICC and actively seeking their investigations of international crimes in Palestine in the first place.)
But since independence will have been established, they'll have to deliver on boring day to day stuff, without constant Israeli abuses like the cross-border sniping and the vetoing of all-Palestine elections that would include places currently administered by Israeli occupation authorities, etc., etc., etc.
New states formed by regional/ethnic separatist/independence movements often elect the political wing(s) of the group(s) that fought the prior government/occupier if independence is acheived after substantial armed struggle. This is usually far less of a problem than in actually revolutionary regimes that overthrow amd replace a central government, because there is usually less ongoing struggle against those invested in the old regime to justify post-victory war government, providing a pretext for repression and deprioritization of economic progress and QoL improvements for the citizenry.
I also question whether Hamas would recognize some other party winning the West Bank, or accept another party's authority over Gaza, so it might have to be a three state solution, not two state.
And I'm not optimistic that, faced with trying to govern Gaza, Hamas would turn the "wipe Israel off the map" parts of their charter into "eh, that's just talk from the old days".
Worse: Could Israel trust that Hamas would do that? After October 7?
So I think that you are being more optimistic than data warrants.
World War 2 is also a weird time in history to gain independence as external forces (particularly the Soviet Union and Western Allies) played a large part of the resistance. If you compare instead with Vietnam, which also was liberated from the Japanese Empire, but was promptly re-colonized by the French, where the same liberation movement that fought the Empire, also fought and won the French, and became the legitimate government of first North Vietnam and finally all of Vietnam. The Communist Party turned out to be a much more functioning government than the South Vietnam Government which had a series of Monarchs, military dictators, western imposed dictators, etc.
Finally I’d like to turn to FLN which is probably the most relevant comparison. FLN consolidated Algeria as a one party state for the first decades after independence, and it took a whole other rebellion for democratic reforms. But the terrorist activities of FLN (which were much more numerous and destructive than Hamas’) almost completely stopped (I don’t remember any post-independence terrorist activities of FLN actually).
I actually think that Hamas’ rule would be far more democratic than FLN’s. Hamas has a wide support among the people in Palestine, and they would easily win a fair and free election. If they would engage in undemocratic activities, it would cost them more then they could gain (granting international recognition [which honestly is unlikely]). All of this would be void though if Israel would continue interfering with an independent Palestine.
North Korea is not the result of a country electing the leadership of an independence movement after an armed struggle.
It would also be very bad if. say, an outside power occupied and imposed a totalitarian regime on all or part of Palestine, and continued supporting it for decades.