Herbs will probably take a little dip considering its the end of DEW. However, they will not crash if everyone stops "undercutting" people. Just put them at a reasonable price (a few gp under med) and let them sit.
All items go through a natural wave pattern, most herbs were expected to go down besides the end of DEW. In a couple of weeks they'll be more stable, especially if JaGex (hopefully) starts banning all the sorc bots besides mine