Yes, 手指會變形 (flatter) and there will also be a lump.
My girl has been sucking her thumb for 4 years. She only did it when she needed to go the bed. A month ago, she stopped (after I told her that she is a Big girl and should not suck her thumb anymore). There is no problem of her getting rid of the habit. Though ocassionally, she still sucks her thumb unconsiously at night