Look at that unique and skyrocketing imagination and immersion there, those detailed responses... but you can't help but respect their honesty and giggle a little.
Well, since this is pure fantasy, I'd be a Sister of Battle, riding in my Immolator and burning everything even remotely heretical to cinder and ash, then proceed to the next. Though I'd like to switch to a Multi Melta every now and then for shits (heretics) and giggles (me). And since it is unlikely that I become a Living Saint just with my flamethrower and melta gun (since Big E prefers rabid mistress types than pyromaniacs), I'd either die a violent death in time or maybe, just maybe live long enough to retire from active duty (if there is such a thing at my appointed Order) and haunt my neighbourhood with a hand flamer, ready to purge heresy and set things on fire. Though at some point I might become bored and disappointed with my aging and failing body, so I'd ask for a suicide mission and probably die. In case I wouldn't, I'd keep doing it 'till I die or become the first Living Saint with a twin-linked Flamer and a twin-linked Melta gun.