I think the readiness to start booing the team might be the real issue actually. With Bale, or with a replacement like Lamela, fans would for the most part be fairly patient.
If he goes without being adequately replaced, it will end the window on a loud negative note, and a lot of fans will be pissed off and waiting for an excuse to vent.
It was brewing early last season after we downgraded on Modric and VDV, until we started scraping together wins. It would be significantly worse if we didn't bring in a decent replacement for Bale, and I wouldn't really blame any supporter for being pissed off with Levy in that scenario.
I don't think a window closing on a negative note is anything new, I think its been quite normal with our recent transfer windows (both winter and summer)
I don't really think the fact Bale went and wasn't replaced would have any majorly significant impact on the level of discontent from now or the time Berbatov was sold, or Modric, or the number of windows we went without signing a striker we all knew we needed.
I think if he went we'd all be pissed even if he were replaced, more so if he is not of course but I don't think it would be particularly worse than say last year when Modric was replaced, Harry sacked and Mouthino the Modric replacement failed to materialise - don't get me wrong that was bad and would be terrible again but I don't see it being any WORSE than that (or the time we sold Berbatov and went 8 games without a win)
Results will dictate the crowds mood more than the ending to the transfer window - start with 3 wins and everyone will be optimistic and cheering on the team (with or without Bale) start with 2 losses and a draw and the crowd will be booing (with or without Bale)