How much does the season soft reset change your MMR by? Also does LP decay also decay your MMR?

I havn't played in 8 months, I quit sometime last season when i hit Plat 5 and decayed to somewhere in gold. Not sure where exactly but i hit gold as i logged on and saw the gold border. If i where to get back into league and play ranked would i end up in gold from having plat MMR last season or would i drop down to silver because i decayed? as im not sure if LP decay drops MMR. I would assume it doesnt and i would end up in gold since i was plat last season and it was only a soft reset.

"EDIT" Poor GD is gone it seems aswell :(