If I'm assuming here you mean Space Mountain? And that is "Tier 1" i.e. not part of G+. There isn't a situation where "G+ users have all the standby VQ reserved". G+ can't reserve anything. Why would standby close aside from park closing? The whole "VQ" was a possibility discussed from the DLP system, but hasn't been part of the WDW Genie announcement discussion at all AFAIK.
ETA: perhaps you are discussing Tier1 rides that would be *boarding pass* only, like RoTR. In that case, if all the passes are gone, and the "individual attraction" purchases are sold out, then yes.. too bad so sad... unless for some reason they get through everyone significantly before park closing that they open standby...