Team signed Thomas Howard last week. He was a WLB for the Raiders then Bengals, but tore his ACL early last year and was replaced by Burfict. I haven't heard anything about their plans for him, it could well just be a depth move or to replace Nicholas/Gaither at SLB. Looks like they used Worrilow there instead last week (or played mostly nickel), as he was in on 94% of the snaps (Bartu 100%, Dent 37%, Gaither 6%, Nicholas 0%). Note that Dent wasn't 100% healthy.
Weatherspoon is eligible to come off the IR by week 11, but I haven't heard anything about his recovery. If it was a LisFranc, he won't be ready, but seems like they wouldn't have wasted their short term IR slot if they knew that.
Bartu still got all of the snaps after a rather poor game vs the Jets before the bye, so that's a great sign that they will continue to use him at WLB and in the nickel. Haven't seen his PFF grade for Week 7, but the defense in general is still playing poorly overall, so I would not be surprised if more changes were to come.
In short, use him now, be ready to replace him later.