Will remote working have a marked increase post-Covid-19? Yes.
Will working 5 days a week in the city centre office decline dramatically? Yes.
But will cities decline? Not at all. They will become even more important -- with a far larger talent employee -- and offices in the suburbs will continue to die.
Instead, large connected cities will become the central-point for an ever increasing number of companies. People need to get together, need to sometimes see each other face-to-face, and that need won't go away -- so instead of seeing each other every day, there will be remote working and then the occasional/regular getting together in a well connected city. The city will flourish not from every-day offices, but from working and networking facilities for people who need to see each other. Most likely subject matter experts will be dispersed and occasional, while middle and upper management more likely co-located in the city. That, by itself, will change how people view the in-city or remote-working trade-off.
Suburban offices? Dead, dead, dead. Why limit your employee pool to a small area in the suburbs, when those same people would probably prefer working from home? Instead, base yourself in the city with flexible offices and hire from an extremely large area. Let people work from home with the occasional trip into the city.