They could do pretty much anything even if it's based on Sice.
Absorbing malice when killing obviously doesn't work, so they can change that to anything really. Not that I can think of many ways other than what others have mentioned here. (Need better imagination)
Everything else for Sice is just "does damage" either on a target or aoe, or has elements that doesn't work in FFXIV (like pulling in enemies).
As for losing malice when taking damage... Well, that's the kind of mechanic I think they would never add to any job. They are already trying to negate the few weaknesses certain jobs have in different situations, and having a job that is so dependent on the fight mechanics... That's not happening.
Also, it would be way to punishing for you to lose a lot of malice from damage, like, way way to harsh considering how they have raised the skill floor in the past.
If it only makes you lose a little malice, then it most likely wouldn't make sense to dump it all (wild speculations here) every couple of seconds (yes you often are hit very frequently). Instead it would just become a punishment for being in a specific fight, and it doesn't sound fun at all. A punishing mechanic should at the very least be interesting and fun.
Edit: They could at least make it a little different to something like kenki for SAM, by not having a requirement for malice built up, to use the abilities, and the damage is then based on how much malice you have.
That could make things feel more smooth when trying to adapt before or after boss jumps or something.
