With Trump coming on board, it looks like the UN has finally overplayed its hand and will pay a steep penalty. Yes, Israel and America need to jointly leave the UN and tell it to get off American soil.
The only reason I can think of to stay in the UN, but not fund it, is the US veto on the Security Council.
Without the US veto the remaining nations can pass all kinds of stupid things that may put US citizens at risk of arrest/prosecution in other countries. Killing anti-American resolutions is the ONLY reason I can think of to stay involved. People with more knowledge may be able to overcome that concern and say we should still get out.