Lets say I get promoted from Bronze to Silver in preseason 2015, I am aware I cannot receive rewards at this point but if I get promoted to a new tier will I stay silver in season 5. Or can I be demoted back to bronze, does anyone know?
Well, it resets for the next season. At the start of next season, everyone will have to redo their 10 placement matches to determine where they get. This can either be a "hard" or "soft" reset. If hard, it will start you from scratch again, just like your first time. If soft, it will take into account your MMR at the end of the preseason. So for example, if you are silver with a silver MMR, and do well in your promos, you will get placed into silver. If you are silver but have lost a lot of games and have a bronze MMR, you will get placed in bronze most likely.
Also, you can get demoted at anytime. Your MMR has to be really bad, though. If you are silver 5, your MMR has to be all the way down to bronze 5 to get demoted back to bronze 1. Hope this helped.
Similar to the other response: The point of preseason is to raise your current MMR so that when you do your placements, you have a better chance of getting a higher tier. Now that you are silver V, you can technically place in s5 or higher depending on your current MMR. Hope this helped :)
if they do what they did last season they "normalize" it. In other words your MMR does not completely reset, instead it gets "shifted" closer to the median. I think this is so ranked is n't a COMPLETE joke during preseason and still has some impact.
preseason 4 - season 4 fact : soft reset.
i was climbed from bronze 5-> silver 5 ( 300 win in preseson 4 success - i did it ) and then season 4 start = even with 7/10 in placement matches , i starting with bronze 4 . well cant complain, its game. so for me, i better explore and learn the new League gameplay (new objectives, items) in preseason , i probably begin ranked when season start.
this quotes bellow also true :
not guaranteed, it all depends on your current MMR which is now Silver
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The point of preseason is to raise your current MMR so that when you do your placements, you have a better chance of getting a higher tier.
preseason fact : " Inactivity decay will be disabled for the duration of the preseason."
PS : sorry my English Op , 
