However the day will come when Whatsapp is down. Before that happens take a look at Telegram, install it and start to use it.
With Telegram you can do exactly the same as with Whatsapp. In addition, Telegram is available for both mobile devices and desktop/laptop computers. No matter if you are using Mac, Windows or Linux - Telegram is always there. Even a web-based app is available. Check out Telegram web page and see for yourself that all major platforms are supported.
Edit: there is also a portable version of Telegam for Windows. You can install it on USB and use it anywhere. Download it here. I haven't tested it though. Use it at your own risk!
Other reasons why you should switch to Telegram:
- Messages are heavily encrypted
- No ads, no fees
- There is an API and protocol available
Telegram app on OS X 10.10 (Yosemite),
all my friends are still using Whatsapp...