My family and I started using whatsapp about 5 years ago. My daughter was in Singapore, and whatsapp allowed cheap phones calls without international charges. Recently, we use it as a group text and picture app. I get frequent pictures of my grandson.I've never heard of whatsapp. Unfortunate for those that have to rely on it.
Having whatsapp down for 6-8 hours didn't cause any problems. I'm sure there are other/better apps out there that do the same thing, but I haven't had the need to search for one.