The cops probably would get called, they might shoot. Police is trained to shoot to disable, not to kill. Sometimes they need to of course. Then if there is any doubt they would be prosecuted and jailed if they overreacted ( this happens ).

Of course these situations are extremely rare as Western Europe is not as a violent society as the US is.

edit: to add: private citizens carying tasers ( let alone guns ) around is unheard of / extremely rare.