How many games can you lose before demotion

depends if you have already been losing at 0 lp

after promoting you have a fairly big grace period where you can chain lose games highly advised not to do so or you will be winning 10 losing 30 for a while

usually 2-3 games since you are already on a losing streak your MMR would be tanking heavily if you have been losing on 0 lp winning some and then losing again

you might eventually demote from THE game that gets you to 0 lp

From tiers it's harder from divisions it's easier

A pro tip Playing to win will net you more wins Playing to not lose will net you a 50% win rate Playing to lose will get you demoted