Based on lots of available International Saver Business seats over the next couple weeks it certainly appears that business travel (at least global travel) is already off significantly. My domestic flight (on what is primarily a leisure route) was full on Monday and I was first on the upgrade list but didn’t clear into F as a GS. I suspect most of the passengers on my flight booked their tickets before the current crisis was much of an issue.
I think some type of bonus promotion is likely later this year. In addition to the just announced waived change fees for tickets bought in March.