yes well there was a time we made stuff out of metal. I would hope that RCD's were brought in by the tie double insulation came about. These days any mains system is supposed to be protected by RCD's, it can't be all ways, a set system has to be followed, either way contact with a live part is dangerous, if in the case of the drill the fault will remain unknown and a breached wire in a wall could catch fire later, if the drill is earthed the RCD will cut immediatly alerting to the fault, if you were to touch the live chuck (that now will be live as not being earthed) then YOU will be the path for the earth fault that blows the RCD, if there is no RCD you'r be dead anyhow.
With no RCD and fuses only the drill bit/chuck not being earthed will not provide the fault current to blow the fuse, You touch the live chuck and it will kill you because it takes just 30mA to kill you and the fuse blows at 13 A - your long dead by then.