Passenger amenities are a very, very small portion of an airline’s cost. When you’re facing a dire situation, as United and it’s peers are with net bookings down 50-100% depending on region, you go after the big rocks. That means planes will be parked, flights cut, and some staff laid off or furloughed.
Load factors are - and will be - so low that cutting amenities would save hardly anything.
Some other facts to add context: Kirby has been very clear that while United will act aggressively to save the airline and employees’ jobs, he sees this crisis as an opportunity to take share from other, weaker carriers (ahem, AA). While there will be big capacity cuts, there is still a view to the future. Also, MP is United’s biggest asset and they know that’s a piggy bank they may need to tap in the future. I think care will be taken to avoid pushing elites away, though corporate travel is currently dead.