This is all 'as I understand it' so feel free to clear up any misconceptions ...
Wade's base defense has 2 ILBs - a 'Mo' and a 'Mike'. The Mo has stronger coverage skills and the Mike is stronger in run support.
Last year Littleton played Mike and Barron played Mo. Both of them have stronger coverage skills than run skills and that was one of the reasons the run defense suffered.
This year Littleton is playing Mo and Kiser and Hagar were battling for the Mike. With Kiser out I think Hagar will be the Mike. But we'll see how that plays out.
With that being said I think Hagar will only be in when the Rams are in their base defense. If it's a 'passing down' Hagar will likely come off the field and someone like Allen or Howard will come in simply because they are better at defending the pass than Hagar. As a result Allen or Howard might get a lot more snaps than Hagar, but it won't be because they beat Hagar out for that Mike role, it will be because the Rams won't be in their base defense that much. (I've seen 30% of the time in various reports ...)
AlbaNY_Ram