Yes, Marriott does have a soft landing in their program. If you fail to make your status for the following year, then you should drop only one level.

As for the roll-over nights, you only roll-over those nights in excess of your current tier status. So if you don't make your status for the following year, then you should have no roll-ver nights.

Of course either of these programs can change at any time, so do the best you can and hope MR plays well with others.

Good Luck.