Not much if any will be lost. Most FTers will simply circumvent the Spend by charging $25k on the UACC they still will have to fly 75K. What they probably wont do is fly the extra 25k they did, so either others will be able to grab a sale fare or UA will end up selling for higher fares in the end then a G fare
and for all the doomsayers UAL is back up to just under $33 a share