Yes it was a terrible year, but by the standards of the era only due to the extent of the Le Mans catastrophe, which really was a tragedy in waiting, ditto the Dundrod TT, where three drivers died.
Otherwise the death of Ascari and Vukovich were just the usual collateral damage, Indianapolis was always potentially lethal and fatal crashes during practice and the race were regular occurences more or less up to date, albeit now far less often. The same applied to all races across Europe and the UK for decades, 1968 stands out as a particularly dark year.
The demise of the Swiss GP was inevitable, the Bremgarten circuit had a fairly savage history and the Swiss government were not comfortable with this and banned circuit racing in Switzerland, but not hillclimbs, plus of course the circuit was prime building land and most of it was subsequently built upon complete with roads and all the usual paraphenalia of population increase.