In a full SIP deployment where agents are login via Genesys SIP server with SIP hardphones, will agents loose functionality of their SIP phones when their PC shuts down ?
Will agents still be able to have calls routed to them if their PC is down ?
Can new agents (without PC access) login via the SIP hardphone ? How ?
SIP Phones will work as that, SIP Phones. If you close GAD or PC shutdown you will lose connection to the TServer and Genesys will not use it as a route target.
You can route to places rather than agents but will lose control of agent statesā¦
No, you canāt login using only Hardphone, you need a PBX with ACD features to do that
Actually, not entirely true. You can configure how SIP Server is handling client disconnects (PC shutdown/restart) by setting option logout-on-disconnect. By default it is set to ātrueā and agent will be logged off. If you set it to āfalseā agent will still be logged-in in sipserver, so call can be routed to him. But as cavagnaro said - you will loose control of agent states.
On Polycom SoundPoint IP series you can map hardphone agent status to relevant TLibrary events. So you donāt need GAD to login/logout/withdrawal agent. If I remember correctly login/logout also works on Aastra 55i with the same method. See āMapping Polycom Agent-Status Updates to T-Library Eventsā in SIP Server documentation. On some other phones you can try accomplish the same if phone support http or xml. Saying that you canāt login using only hardphone is a little too much 
thanks for all the advise guys!! this info is excellent !!