If UNGA would create, vote and pass a resolution to unseat Israel from the UN, there is little the US with their veto power in UNSC could do about.

Israel would most certainly spit venom and either withdraw voluntarily or make itself a clown and challenge the decision before the International Court of Justice.

Given the fact that any country can delay the ICJ by filing a opinion, it would take years or decades before the court can actually decide.