Someone losing 100% of his investment is possible if the altcoin an investor picked and hold lost it's value and dumped to 1 satoshi with a huge buywall. In waves case, you are right that its not possible for it's holder to lose 100% of his investment since it has retained it's value even if the price dropped big. Investors have lost a huge percent of their investment though even if waves still have value. Probably waves would pump soon after hardforks of bitcoin stop.