I can tell you that seniority, tenure, and vested status were definitely not the keys here.
There are 20+ year employees who are furloughed, and in the same group, 1-year newbies kept.
There are directors and senior directors gone, yet some of their direct reports remain in place.
The chop did seem very haphazard, to be honest, with very skilled people tossed out and in some cases whole support groups for live production systems decimated.
There are sad jokes going around: "Dang it, I have to STAY." Life will s— for both them and for the furloughed as well. The furloughed won't have a house anymore; those staying will be worked to death for 20% less and never see their house. (New 4-day work week be damned, says the VP!)
To the company's (meagre) credit, they continue paying 20% of salary to furloughs for the 60 days, which should usually cover med insurance/etc. That's not charity – the company, if things recover or at least stabilise by then, will need them back because the cuts went too far. Some might not want to go back if there is ANY other job they can go to instead, given the treatment they've endured over the last few years. But most of those who haven't bailed for good by now are probably stuck there for a reason.