你的问题不太清楚，如果是 the number of people remained unchanged.这样的句子太多了。指人的数量不变。你如果想问people who + remained unchanged,也就是说人做主语，能不能接remained unchanged, 这要看上下文了，比较少见，但也有。如：

Stephen Acabado debunks theory that the people of Ifugao remained unchanged for 2,000 years