The Tallboy bomb was considered so valuable that bomber crews were ordered to return them to base if they could not find the intended target. That was a special case though.
For large-scale attacks, bomb crews were given alternate targets if the original target could not be reached or turned out to be under cloud cover. Scrubbing a mission wholesale (or dumping the bombs into the sea) because the primary target was obscured would mean having put men and material in danger with nothing whatsoever to show for it -- a huge hit on morale.
So, generally speaking, bomber crews dropped their bombs, near their assigned target, or on an alternate target.
As for your specific questions:
Flak was a "when", not an "if". Any target valuable enough to be attacked by bombers was protected by flak. Generally though, flak was placed around the target, not at the target, and spaced apart. From altitude, finding and hitting something like that was next to impossible. Getting lower to increase your chances makes you a much easier target for flak (both the one you want to find and for everyone else) as well as enemy fighters. ThisAttacking a point target like this was only done by highly specialized units with lots and lots of prior training, for high-value targets (think Dambusters). Not something a crew, or even unit, would decide to do ad-hoc after a scrubbed primary target.
Hitting the general area was what they were trying to do anyway -- even the USAAF was lucky if they could hit the correct post code, and that was for successful attacks. (The whole "precision bombardment" was the propaganda shtick. There is nothing "precise" about a four-engined bomber dropping dumb munitions from 20.000+ feet of altitude.) If the target is under cloud cover, chances are you won't even find the correct city. Also note that the Area Bombing Directive was a thing of the RAF, and had been superceeded by the Cassablanca directive in January 1943.
See above. Usually the bomber crews would have a secondary target assigned. I would guess there's artistic license going on here (unless someone can dig up information on the actual bombing mission...).
As for precision: The USAAF considered any bomb that hit within a 300 yards radius around the aiming point to be "on target", and precious few bombs even got that close. Sources differ, from anything between 7% coming within 1000 yards to 20% being "on target". That means even the optimistic source states that four out of five bombs missed by over 300 yards...