The partition plan was a compromise that neither side liked, but the Jews accepted and the Arabs did not, with the latter starting a war with the express purpose of "driving the Jews in to the sea". Which Jews would be allowed to stay, if any, was never made clear but the general consensus would be only those who lived there prior to WWI at the most. In the period following WWII there were numerous expulsions and population exchanges in to the early 50s. Ethnic Germans from parts of Czechoslovakia and Poland, various ethnicities from territories the Soviets acquired, various Central Europeans such as Hungarians moving across new borders, Japanese from Manchuria, Formosa, and Korea, and the whole Hindu/Muslim business on the subcontinent. Apologies to other groups not mentioned. These movements were a combination of outright expulsion, voluntary migration to avoid repression (real or expected) by the majority inhabitants, and so forth. Some of these exchanges were abrupt, some a little more protracted. Basically with 3-5 years after the declaration of the state of Israel roughly equal numbers of Arabs (almost all Muslim) had left the territory of post-war Israel and Jews had left the territories of the various Arab states. Most of the Arabs who left were those who decided to leave, whether on their own or encouraged by the Arab powers to get out of the way of the conquering armies, and most of the Jews who left were specifically expelled by various Arab governments. In the case of the Arabs, yes there were those who left/were expelled by violent action, and on the part of the Jews there were those who left on their own. The bulk of those who left their homes were as described, voluntary refugees on one side, expellees on the other.
It is worth noting that the Arab Palestinians lost 100% of the territory given to them under then partition plan, that's right 100%. Some they lost to the Israelis and the some to Egypt and Jordan, which occupied the parts of the Mandate under Arab control at the end of the fighting. From 1948/49 until 1967 you could have had the same Palestinian "state" you see today (actually a little larger) with the West Bank and Gaza (part of Jerusalem and other bits annexed by Israel after the 1967 war included). When Egypt and Jordan gave up their claims to territory occupied in 1948/49, it was after they no longer held it, a point often ignored.
In any case if you fight a war, whether or not you start it, whether or not your cause is just, and lose, there is always a price to pay.(1) Returning to a perfect status quo antebellum almost never happens (would say never but who knows). Of the four wars (48,56,67,73) the Arabs started three and the one they did not start (1956) was precipitated by the nationalization of the Suez Canal and only resulted in a return to status quo antebellum (more or less) due to the intervention of a rather powerful outside party (the USA). In 1973 the negotiated settlement did restore "lost territory" to Egypt, however a peace treaty was concluded, the area was demilitarized and monitored so both sides had gains. The reality of the Arab-Israeli conflicts is that you fight a war and lose, you pay. Always has been that way, always will be. Is this fair, maybe maybe not, but as Jimmy Carter once opined in a rare moment of clarity, "life isn't fair".
(1) Both sides in any war claim that they are fighting in a just cause, nobody ever tells the poor schmucks who have to fight and die "you are fighting for some immoral or worthless cause". The grunts may know or suspect this, but its never explicit. Remember that until the end of WWII the German uniform belt buckles had "Gott mit uns" on the inside.