They have to ask their voters about budgeting the next fighter and swiss people have said no before even to the "cheap" Gripen.
Last time, the Gripen was subject to something of a smear campaign by its competitors, dubbed the IKEA Fighter among other things. So while the referendum was on the financing of the procurement, it became a de facto vote on the Gripen itself. Next time, the government has changed the rules slightly in that the referendum will be held
before a platform selection, and this should remove the incentive for any of the bidders to undermine their competitors (and by extension, the requirement itself).
As has already been said, the Swiss traditionally are very pro-defence and so I would imagine any future plan to buy new fighters would pass.