[throwawayboise]

It would be a lot of work, e.g. just the plumbing for residential (kitchens and bathrooms in every unit) would be very different from plumbing for offices (a few central toilet rooms).

Electric, HVAC would be similar.

However, still could be possible in some buildings and ultimately be worth doing. For other properties it might be cheaper to raze and rebuild rather than try to fit residential space into a commercial-plan building.

Completely agree with other posts that the risk of loss should be squarely on the owners/investors. Property is an investment like anything else, and may lose value. And I'd guess commercial property is riskier than residential.

[mlyle]

Just converting a very small share of buildings to mixed commercial-residential might be enough to adjust for the reduction in office demand.