No. It's wouldn't be a virtual memory issue. In the event when it does happen all we get error messages
such as Server aborted trying to recover by restart"
The "Working Set.." messages sometime precede the restart. It's not really about virtual memory per se. It's that the available RAM can get filled with multiple documents, user sessions and cache. Those messages indicate that QVS is having to manage the RAM.
" The one issue I would have is with Document Chaining as there would be an extra cost for licenses for every user who uses this application and accesses the chained document?"
The chained document does require a license. Only an issue if you are using Doc or Usage CALs.
Expressions that reference fields from two disconnected tables generally cause a temporary table of the cartesian product to be built. In addition, data islands frequently have a negative impact on cache. See