I have some thoughts and would like to share here.
1. EnodeB RRM or application may have max # of users context. It may depend on the various factors like memory, license etc. It was all about the # of users context can be created and maintained at eNodeB. There is an another factor "availability of radio resource" at a particular point of time. Some times RRM or eNodeB-app may take decision to delete a particular UE context to cater a new user in the system.
2. W.r.t core network, GTPv2 has TEID 32 bits long , so by calculation a node can create maximum of 2^32 - 1 , TEID-C.
Whatever I mentioned above, it may correct or not. I am looking for other professionals to respond.