I’ve actually never had Bacopa Monnieri (moneywort) as a plant before. Though I hear it’s not a very demanding plant to deal with. It is just like other stem plants where it can still grow by floating. Having said that, substrate will create a better nutrient source for the plant. If it does become unrooted, you can always tie a small rock to it and then stick it back in the substrate. It will sooner or later get a root system to stabilize.
Trimming the plant and re-planting the clippings is a good idea as well. Seeing how there is less weight to the actual plant, you can plug it into the gravel and typically the small clipping won’t up-root itself.
If the moneywort is browning or yellowing on the new leaves, then you might need to look into getting some root tabs to get some nurtients to the plant. (this is typical if you have inert substrate)
Video: minimalist iwagumi by George Farmer
Mr Farmer always manages to create spaces that attract my gaze. You won’t feel deceived with this video - 100% recommended.