Who do you have for your other QBs? If you have Bulger and Warner, you definitely should keep them both, because they could switch them again in another week or two. If you just have Warner and not Bulger, you're in a sticky situation, and really have two choices right now.
One choice would be, if you have the roster space, wait a few weeks, and see if the Rams switch back, hoping you'll still get some value out of him. If you don't have the roster space for that, your only real option before you consider dropping him would be to offer him to the Bulger owner in your league as insurance. You would get next to nothing in a trade, but might be able to snag a useful bench player from the Bulger owner. That's better than getting nothing.