The referendum was set up that way specifically because Cameron felt he couldn't lose such an "extreme" choice, and then when people voted for less EU - as they always do in every country - the question would be sufficiently vague that it could have been ignored. As it always is. The binary choice was really quite a stroke of luck because it made it impossible for the government to pretend the decision had been implemented when it hadn't been, despite obviously being desperate to do so.

As for the EU being "forced" to accommodate, that tactic was also tried. That was Cameron's pre-referendum negotiations. It was a total failure, he was rebuffed on everything and hardly talked about his supposedly great deal after he returned because it was clear to all that the EU had compromised on nothing. Both during the process and after it, the EU's position was always the same and boiled down to "we don't care what voters think, you obey entirely or quit and accept that we'll blank you from then on".