Put out (Extinguish) the fire just after a while or else(otherwise) it will spread all around. After saying this, he walked away; but he had no idea, whom he had said that (so), had the whole focus on playing games on mobile. Though, he should have extinguished it (put it out) himself, but still, it doesn’t mean that the other person doesn’t even care. If I hadn’t noticed well before time, it could have been devastating/fatal/hazardous/dangerous/ perilous/precarious/unsafe/threatening.