I am genuinely interested on how this will be handled, if something like that happened now.
There are a lot more transactions being done now and
I wonder if miners would all work together to "rewind" the Blockchain, if it happened again. I think it is in everyone's interest to do this again, because
losing a few coins with a "rewind" is better than losing the value of every other coin you own, if miners did not want to participate. Fortunately for us, a
lot more eyes are currently on the Open source code and also on what is happening on the Blockchain, so it will even be spotted a lot quicker now.
The only way it would happen again is if they did a soft fork that had mistakes. Most forks carry some mistakes - the last steem fork had so many bugs they had to rapidly release fixes - luckily in the steem universe the top twenty witnesses decide what version to run, so it's easy to correct.
With bitcoin it would be much harder given that the miners are numerous and you'd have to persuade them one by one to run the corrected version - that's kind of why the devlopers are so resistent to "improvements" and are so conservative about soft forks. Forks carry loads of risks.