Earlier quoted context omitted.
What reliable alternatives would you suggest?
That very much depends on what are your requirements. If you need all the stuff skype supported originally - chat, voice, video, screen sharing etc. then I don't have a solution I'm afraid, particularly if you need support for various operating systems. What we need for the internal communication (within the company) is a simple IM, integrated with ticketing system (a bunch of generic rooms, per-ticket rooms, linking…
Google Hangouts.