If your organization has already invested in Lync and its infrastructure, it's hard to imagine them giving up on it unless it has major issues.
Of course there are other options, but it's not like Lync is going away anytime soon, and Lync 2013 recently came out so it is still being invested in by Microsoft. And there is a wealth of information/documentation/communitry (i.e. TechNet) around the Lync SDKs, so that is also a bonus.
Also, Lync is built on top of SIP and well-known media codecs, which are not proprietary. (their SDK is proprietary, of course)