The SAA 747 Heldeberg accident near Mauritius...
Basically re-certifying a combi is prohibitively expensive I believe due to the fire suppression system. The only ones that exist are ones that were built as combis (I.e KLM 747s). I’m sure someone will be around to give you more detail. But yes, in these times having a fleet of combis would be ideal although for how long who knows.
champ