That's probably completely wrong. The patent landscape has changed dramatically in the past 5 years.
The likelihood they could extract significant sums of money from these patents drops every day.
I mentioned this in another comment but how does Yahoo even know that its intellectual property wasn't taken?
Is it unreasonable to suspect that a company that has had multiples breaches of security of this extent might also not have had its IP taken out from underneath them as well?
when you patent something it's always in the public domain, that's the point of patents, except that the ownership isn't public domain just the knowledge of a particular tech. but yes, nothing guarantees that tech they had in the pipeline isn't being stolen right now.
but if the details of a patent have been stolen the patents still have value, except for when the exact implementation of a patent can be circumvented due to access to plans.
First assumption, other costs are negligible: no, I'm not. Every dollar spent on salary is a dollar that doesn't go to profit.
Second assumption: letting 80% of staff go won't hurt. For that, I simply have to describe what I've heard from friends / coworkers / scuttlebutt about working at yahoo. But there are a lot of eng doing maybe a couple hours of work per day.