Regular readers may have spotted that Windows 10 Mobile itself got an extension from Microsoft, in that support now ends on Patch Tuesday this month, rather than last month (December 2019). And shutting some things down does tend to ruffle a few feathers and extensions get asked for. In this case, Whatsapp for Windows Phone was supposed to stop working yesterday, as I write this, but it seems someone's relented at Whatsapp and a further fortnight's margin has been allowed. See the screenshot below.
Now, it's only a fortnight, so don't get too excited. I'll watch this and report back if it gets bumped again.
Meanwhile, now's a good time to think of switching to Telegram (Unigram client) if you want to carry on using Windows 10 Mobile with instant messaging to others.