I hope Skype dies (though I also still depend in it). I'm currently trying to get our project on Teams which works much nicer (it's MS' Slack clone). Wouldn't hurt to have that on Linux as well indeed although Slack work perfectly on Linux.
If Skype dies we basically have no alternative. Sure, you got Slack, Hangouts, Teams (as you mention), the new Atlassian thing etc. but that's mainly for group efforts or for a company setting. Skype isn't used just by businesses. I mainly use Skype for videocalls with friends and family, usually one-on-one, and for that we have zero replacements.
Slack is just not a thing for this use case, same for all the other collaborative tools. Hangouts delivers subpar video quality and decent audio quality (if we ignore the fact that it hasn't been working on Firefox for a while). Appear.in glitches and lags a lot, sometimes to the point that is not usable. Signal would be great, video and audio quality are amazing on mobile, but there's no desktop client (apart from a Chrome extension that can't really be called a desktop client). WhatsApp video quality is very poor while audio tends to be decent, but once again, no desktop client (there's an in-browser web app with no support for video calls). Skype too, is fine on desktop, but it's a huge resource hogger and consequently battery drainer on mobile (the only non-game app that manages to warm the back case of my Android phone).
So yeah, future doesn't look great. I am hoping in GNU/Ring, but who knows...
