yikes...

do you know why you got stem rot?

definitley take cuttings...
becareful with the rotten area of the plant... treat it like nuclear waste.. my concern is that it is a mold or fungus with spores that can spread around....

your enviroment needs to be condusive for this shit to grow... so you should probably make some enviromenatl changes with your next grow...

your fluorescent lights will be fine for cuttings

: )