If you read "Shape Up", you will realise there is a _lot_ of slack at Basecamp (I know, I've implemented it myself in one company), and a lot of space to think things through. Tons of autonomy.
6 months pay is not a good bargain for a great job.
It's a superb bargain for a job that has suddenly become very uncomfortable.
Of course putting 50% aside is huge but I think 20% is achievable and will still create in one year a couple of months to live without a job.
I find myself sometimes hearing people saying things like this “if my company will give me X salaries I will leave” but few will actually do it. I always push back saying how about in the next 6 months you put aside some money and take 1 month unpaid vacation. I listen the arguments why they will not do it and realise people say will leave job if compensated but mostly they dont walk the talk as there are other risks/loans/friends/promises that keeps them there.
Surely some of the employees left for ideological reasons, but 6 months of salary just for changing jobs is a difficult incentive to ignore.
Anyone who was considering changing jobs would have a hard time saying no to 6 months of free pay. The publicity of this situation also makes them attractive targets for other companies looking to hire out of the situation.