Famous example of a comet breaking up from entering Jupiter's roche limit in a highly eccentric orbit (not circular). Spaghettification is also an example of how tidal forces still apply during a head on collision.
Yeah, but single large mass hitting in one place vs stuff spread out vs planet forming a ring and deorbiting over months/years would affect the outcome
Practically, I'd think there wouldn't be a huge effect beyond some CMEs - the mass of the earth is a rounding error compared to the sun - but I'm not a cosmologist