Once you reach perma ban stage it can happen if you don't change your behavior, however if you're behavior continues to improve then yes the level can go down. That said if you went down to chat restrictions only and were incredibly toxic to the extreme Riot can and will go striaght to a perma ban. Don't ever think that just because it's gone down it's ok to be a jerk again..
Riot's done playing nice with stuff like that and now they'll skip steps if they feel you're not going to change or worth the effort so always strive to behave.