character cannot be saved from a roll that takes him out by offering a
concession. You have to offer the concession before the roll that
takes out your character. Otherwise, it’s cheating the opponent out of
Basically, if the attacker's dice hit the table, (or the rote spell is declared since there is no roll involved), it's too late to offer a concession. You can't offer a concession after the dice hit the table/rote spell declared to take you out because your already taken out at that point & your fate is in the hands of your attacker that threw the 8-shift ice lance.
It's perfectly acceptable to offer a concession like "how about the party cripples this guy & takes his candy" as a concession or to being taken out when they only wanted to take his candy. If they are cool with crippling the guy and accept the concession, then there is nothing left to discuss, if they balk at the idea of crippling him & suggest maybe "instead of crippling him we just injure him enough to get him pacified without anything he can't recover from with some time in bed.
As to the group treating it like D&D & going for the insta-kill all the time with their attacks on anything, I had that problem for a while & the solution was to just give the party an aspect of being
known murderers by the folks they were up against for a while. They pretty quickly noticed that people no longer wanted to meet face to face with them without heavy duty overwhelming(when possible) backup/body guards that started shooting if the party so much as suggested a threat. Once they got to the point of & realized that even the ghouls didn't want to associate with them, things started clearing up in that regard & they started getting more careful about not using ultra-excessive force when it only needed a small push.
If all of your NPC's are gong for the kill all the time though, the players are just reacting to your cues. The bouncer at a shady bar catering to bigbads might be able to seriously hurt the party, but he probably doesn't want to deal with the bodies & would rather just give them a bad day and send them packing. If they have just been following your lead, it might not be a bad idea to sit down & admit there was a mea-culpa moment that you would like to work on with their cooperation.
Then of course there is that whole first law violation thing where magically killed mortal= refresh point & aspect warping penalties. Even if they just say the taken out mortal is pinned to the wall by an ice lance through his arm or encased from the neck down in ice with enough room to breathe, bled to death where pinned or froze to death while trapped still counts as magically dead by strict wording. The vagueness in the laws benefit you as both a kind benevolent GM as well as an annoyed killer GM a grudge.