Suspend the league for a bit and work out what to do in the interim. It takes time to plan changes this big, so let's hope the all the major footballing bodies give themselves that time.
Let me predict a timeline.
Suspend all football internationally until June 2020, at which point the seasons of various countries will be given until December 31, 2020 to resolve their remaining fixtures. The Euros can then be held in January 2021, with the following season running from February to November 2021. Another season can then run from February 2022 to November 2022, in time for the World Cup they've forced us to hold in December 2022.