If you don't finish your placements for Ranked by the end of the season, do they reset, so that your placement records are gone? For example, if you played 7 games out of 10, and you don't finish it, does it go back to 0 games out of 10, and you can redo your placements?
Your rank in general resets at the end of the season and everyone does their 10 placements again. However, your MMR and your previous rank does influence who you're matched against and where you're placed. A lot of people just decide to stop caring in preseason because it's gonna reset, but that's an absurdly stupid mindset to have because anything that happens in preseason will affect your next season. It's probably better for you to wait to finish your placements until next season, and why is so that, next season, you don't have your rank lowering where you'll get placed. Everyone gets placed lower than they finished the last season, so unless you're confident that you can climb to the rank you want with it being unlikely that your teammates care at all about the game, don't even bother with ranked in the preseason.
I'd recommend not finishing your placements in the preseason if you have not placed before. Anyone that has been ranked before is subjected to a 'soft MMR reset' which will drop your MMR when the new season starts. Anyone who has never ranked before will be placed solely based on their placement matches (rather than the MMR they got from prior seasons) and will not lose anything from the reset.
