A visa grants you permission to cross a border. Nothing else. Depending on the visa class (or in some cases the exception from the requirement for a visa), Thailand grants a duration during which you are permitted to stay inside Thailand. This duration is indicated in your passport. Extending the permission to stay doesn't extend your visa.
So, to summarize, if you have a single entry visa and show up at the border, you will end up having permission to stay inside Thailand, but you will no longer have a valid visa.
May I ask you if you know what happens if he first gets a 30-day extension and then goes back, pays another 1900THB and applies for another 30-day extension? Obviously, it will be refused, BUT will he get the 7 days "refused application" stamp and as a result, cover the 32 days needed?