Omnichannel Routing - Differenciate Incoming calls from Completed calls

Context: with Zendesk Talk enabled, Omnichannel Routing allows to route only one call at a time (which makes sense).

Issue: Zendesk doesn't differentiate an incoming call from a call which were completed hours earlier, but became a written conversation. Consequently, we can't route tickets which were created initially from an incoming call, as if it was an email ticket. These tickets are not calls anymore and shouldn't be identified as Calls.

Example: Agent A answered to an incoming call but this call needs to be escalated to Agent B. Agent B is currently not available. Thus, Agent A needs to desynchronize the call. Agent A finishes the call with the customer and assign this ticket to Agent B. Afterwards, as soon as the Agent B comes back, the ticket can't be routed to them because Agent B is available via email only and not for Calls. This is a big limitation here, because even if the Agent B is Online for Calls, they will receive these tickets with completed calls, one by one, instead of getting assigned these tickets according to their capacity.
As I said, these tickets are not calls anymore and should be routed according to the Email capacity not Call capacity.