In real football, Tiki is perfectly fine. Check Football Outsiders' stats...he rates as the #5 RB in the league, and one of the guys currently above him is Ladell Betts. So his actual skill is not declining at all.
Also, the Giants just made it through the most difficult stretch of their schedule. Between Indy, Philly, and Seattle, it's a minor miracle they won 1 game even. Don't expect the first-half blowouts to continue, and don't expect the team to fall apart.
The one problem I have with Tiki is Jacobs at the goal line. His improvement from last year to this year is off the charts...remember those FO stats I told you about, where Tiki ranked 5th? Well, #4 is Jacobs, in just 14 carries no less. Don't expect Tiki to get almost any short-yardage work at all; heck, in an interview before the season on NFL Network, he even said something to the effect of "don't draft me, Jacobs is gonna get the touchdowns!"
However, since so many other teams use goal-line backs or committees these days, Tiki should still be top 5 even in non-PPR. He'll be among the league leaders in total yardage again, and he'll get a few long scores. Also, using Jacobs for non-goal-line carries is a good thing IMO; Tiki has gotten a lot of touches over the past couple years, so the relief could possibly prevent him from breaking down.