There was a programme on TV about this a few weeks back, it was really interesting. The suggestion was that the pull of the moon keeps the earth on track - if it went, the earth would start wobbling about on its orbit.
The moon is slowly moving away from the earth but I should't worry as this is not a threat of the moon disappearing for centuries if at all. The moon cannot diappear except via a massive strike from a super-sized meteorite which would be so large that it would probably destroy the earth's orbit. No tides yes. No evidence for the sun effecting tides.